A point to note, when building houses, vehicles and other 3d models, is that many 3d apps cannot assign materials to surfaces/polygons, they can only assign materials to discrete, seperate objects!
What this means is, that say in Vue, I import a building, and it's main walls are all one piece...I cannot assign different materials to each wall surface! So I could not apply a different material to say, external, and the internal walls. This prevents a lot of precision in rendering.
So, when you make models, and go to export them, split off surfaces and objects, and give them seperate materials, so you can then later on chose how to assign materials! :)