I am creating a 3D first person medieval arena by using the soft ware unity. Below I am going to show steps including screen shots off my arena in progress which I will analyse and explain. However It is my first time using unity so creating this 3D arena consists off making mistakes and finding out my own personal technique, So I may make small changes around my arena for instance something In step 1 could be different in a future step.
1: Huts & Arena
I began my 3D level by roughly coming up with a level design which I created before hand on Photoshop. As you can see the Idea is really simple and there isn't any detail but just by doing this basic plan, it generated Ideas on what I want my medieval level to look like.
For instance I knew I wanted a arena in the centre off the level, I didn't have a exact idea on what I would have in this arena but i know i wanted it to be the most eye catching, have the most attention and be easy to notice, wherever the player is within the game.
When I started creating the arena and the basic huts etc. I first started by laying out where I wanted it to go for instance I used different materials/cubes to give different areas a different atmosphere. For instance I wanted the arena to be in the middle off the level with a 'Garden' So i built a simple flooring with a texture on. Next I went into the pro builder window and created a pipe shape which then I gave 10 sides, made it a little thicker and a lot higher and this gave me my perfect circle which I used for the walls off my arena. 
For the medieval 'peasant' houses/Huts I Didn't want anything too posh or too big because I wanted these houses to belong to ordinary people although I wanted to have two different kinds off these houses. I wanted houses which had no door and could be explored and houses which had a door and couldnt be entered, I wanted to do this to give it more off an exploring effect for instance not being able to walk into everything and having to find things. I began by building the four basic walls and using an arch for the triangle wall which I adjusted it to 1 edge which gave it an triangle effect - I used a similar method to get the roof. For the open houses I left the door off and gave the floor a pebble material while for the closed houses I filled in the room and gave the house a door which I created by basically using a new cube and getting a door materiel which then I adjusted the tile size so the door fit perfectly within the cube and the walls.
2: Corner House
I wanted to give the player a 'house' they can explore and run in so I created a two story house which Is large enough to fit a lot off assets in and give the game more freedom etc. I began this house by creating the flooring which I gave an material of a dark chocolate wooden floor.
Once I was happy with the shape off the flooring I then started to do the walls. I wanted to have two 'different' sort off walls on this house for example I wanted the bottom half of the house to be stone and the top half to have more off a Tudor look and to have the front bit off this wall to overlap the stone wall. I did this but I also added some windows which I created by using cubes and a window material which I then adjusted to fit the walls- Similar to the door technique. Once I was happy with the walls etc. I decided to make the second flooring, I started this by creating stairs and then copying the bottom floor and dragging it up to create an identical top floor. To create the roof I used the same technique as the Tudor small houses however I used two and sort of 'Joined' them up. For the decorative items such as the wooden beams and the balcony near the stairs I created an cylinder and Increased the amount off sides to give it more of a circler look which I then i used the same material I used for the flooring and the roof. Around the corner from this house I added three off the small huts - 2 being closed and 1 being open. 
I wanted to design a house which had a weird, fascinating appearance so i did a researched double houses and a joined up house caught my attention. I started this the same way I started the other houses, By doing the flooring and the the walls. I basically mirrored my Movement/Building so the houses was identical to each other. I wanted to add windows to the buildings so I used the same technique that I sued to have buildings for the corner house. Once both houses were complete I wanted to build a sort of 'bridge' which joined both houses up. so when the player goes up the stairs then they will be able to walk across to the other house without having to go outside etc.
Instead off having a regular house with rooms and a second story I decided to add a 'maze' house which is basically a large house with a lot of walls inside the interior. Some walls lead to dead endings and only the right direction will get you to the room in the house which will include some useful assets for instance their could be new weapons, power ups etc. I think doing a maze house will be more exciting and adventures than a usual house with normal rooms for instance If my level was used as a co- Op first person shooter, the players will be able to hide in the maze- Giving the level more dimension and freedom. 
To create this house I knew I wanted a large area but also a basic layout for the building, I started doing this by laying out the flooring so I knew how big I wanted the walls to be. Once the flooring was completed, I created a cube which I then used to create a 'Small' Wall which I gave the material wood and I then proceeded by creating a new block to use as the normal walls which I used the material Rocks which I have previously used on the other buildings. For the roof I created a Prism which i then adjusted it to fit the building to create a appearance of a old, triangle, big-built roof which I desired.
After the building was complete, I then started with the maze inside. I used several walls which I organised to create hall ways, dead ends and then the 'goal' room which will include assets.
5:Building the outside wall & Extra Huts/Houses
Now that I am overall happy with the arena level, I wanted to create a mater, outside wall which will stop the character from 'running' out of the village. I did this by creating a cube and adjusting it to be large enough to stop the player jumping over it etc. I then moved it behind the buildings and then proceeded by creating more cubes to make sure all of the pavements/Flooring makes up. I wanted to put the wall close to the buildings because I didn't want the player to go behind some of the buildings due to lack off detail behind the houses for example their isn't anything eye catching, exciting or even extraordinary behind the houses so I wanted to close that area off. However Once I completed the square wall there was a few gaps, mainly in the corners which i realised Their is enough room to create some small huts, sheds, wells etc. So using the previously techniques for building the other huts etc I decided to create some.
I first began by making a little shed which I mostly copied from the other huts in the village although I made this hut more of a rectangular shape with wooden beams and a straw roof.
Next to the 'maze' house I wanted a house which had the same appearance on the outside- Quite bland. To sort of make the maze house fit in with the theme of the level more. I did this by starting with the floor and then creating the walls and using the same technique to get the roof as i have previously done. However I didn't want it as busy as in the maze house but I also didn't want to leave it bare so I created more walls and put in two rooms within the building, including an entrance and a hall way.
On the other side off the 'maze' House there was stil quite a lot of room although I didn't want to make a building which is too big because didn't want to make it too crowded or to take the attention away from the maze house which is the main house on that side off the level due to the size and originality from the other houses. So I basically copied a hut but enlarged it and changed the roof to straw just like the other hut. Although this time I wanted to give it something extra so I came up with the idea off an outside shelter and a well to give it an image off an garden. I created the shelter by using a block, making it thinner and lining it up to the top off the hut door and I then created a cylinder with 10 sides to give it a circle beam appearance and then gave it the dark wood material.
To create the well I started by creating a pipe and changing the sides to 30 + which Creates a flawless circle, For the wall off the well I made it much thicker but for the water I made it 0.2 Size smaller than the well so it can fit comfortably in the well without no overlaps. For the water I made the piper much thicker so there wasn't any gaps and it was just one solid, thin circle which I then textured with the water material. For the beams and roof I copied it from the hut which i just created but made it much more smaller and arranged it so it looks like its sitting on top off the well. 
All the extra material I have download and used has come from this website:
http://www.textures.com/browse/bare/356
* Changes and adding assets *
For the next couple of steps I have made quite a few changes and imported assets from the asset store. I am going to briefly explain what I have done to achieve the scene/buildings. 
Firstly I changed the 'maze' house into a castle which holds a couple of dungeons and a under 'tunnel' which leads to a room (As you can see in the images below.) I used a downloaded a package which had most of the gates and props such as cuffs and seats for dungeons. I decided to make the dungeon as dark and aerie as possible because I didn't want the dungeon to be seen as bright and cheerful. I wanted it be as empty as possible with a few assets as decorations such as torches, chains, barrels, chest, candles etc. Most of the rooms In the dungeon has a door on so its 'locked' and the player isn't able to go into that room although some of the rooms the player is open so the player is able to explore. 
Behind the castle is a large field which has several trees and a 'shed' which I previously had next to the 'maze' house with a well, however when I changed the maze into a dungeon I thought the shed would look more flattering behind the castle to give the back of the castle more interesting and give the player something to explore behind the castle. In the castle I put in some hay and a large wagon. I didn't want to put much in this shed because I wanted it to be quite simple as its only small. 
In the house next to the castle there was a large hallway which at the top off the hallway I placed a table. On top of the table there is a book and a candle, Under the table there is a chest. In one of the rooms there is a table chair and a barrel and in the room opposite from there is a chest boxes' a barrel, decorations and a table with scrolls, books, candles on. 
In the large double house I put in stairs, boxes, barrels and tables.
In the litle shed at the corner off the level there is a hay, table and a chest within the shed. I wanted to keep it quite simple because I know houses in the medieval times wasn't complex or a lot of furniture as in this times people was struggling to live.
This is one of my favorite houses in the village, I created it so the down stairs off the house is like a bar which has table and chairs, barrels, torches and so on while The upstairs is more off a keeping. It has spare rooms for the villagers which include a large single bed, barrels and lighting.
Here is a video which I personally recorded at home by using a programme called bandicam. I recorded this to show what the level would look like whilst playing the game.