Recently I've been getting frustrated. I have learn to model a half decent model in maya and I export it as an FBX and It simply doesn't work. I add mesh colliders and ridged bodies. But none of it works or keeps my character from going through. I have character colliders placed correctly and all. Also my Walls on houses that I Model don't show from the inside but only outside.
The problem with the collision could be that you have not set the mesh collider to be convex in the inspector. If it is not convex then Unity thinks it should treat your model as a mesh that is forming some sort of plane. What do you mean by character colliders? character controllers? If so then you should either use rigidbodies in conjunction with mesh colliders or a character controller only, not all 3 at the same time.
In regards to the rendering problem with your walls it is a behaviour unity uses to optimize 3D calculations since you more often than not you don't see the inside of a 3D object. A solution you could use would be to make your models like this:
___________ | _______ | | | | | | | | | | | | | |_| |_|
Instead of what you are proberly doing now:
____________ | | | | | | | | | |
where _ and | are the mesh of your walls. I think you can also solve your problem by changing the input settings for you fbx file but that I don't know how to do.
Make sure you don't have the "Trigger" option checked. If "Trigger" is checked, you will go through a mesh, but it will listen to a script instead. If "Trigger" is not checked, you will collide with the mesh, but the script will be ignored.
Also make sure you add the mesh colliders to the individual mesh's , not the prefab, or the groups they are in. You have to get down to the specific object.
Also, if you made your house using flat planes, you can see BOTH sides of a plane by giving it the following material:
Transparent --> Cutout --> Soft Edge Unlit
I hope this helps. Please let me know. Thanks!