This isn’t a question about “rendering in Blender” this is level/asset creation. Lookup Bitmap2Material and if you can’t find a way to get it and refuse to use the demo, Chocofur offers some nodes that will at least do “something” though from what I’ve seen are very lite.
Rendering is about getting an image, creating anything for a game (like your whatever you’re doing) is about creating assets. If you want to make a game, you have to create it with as few polygons as possible or rather don’t over do them.
I’d explain some of that more but if you don’t already know that then you would obviously either not know basics or don’t know what you want.
So before I explain anything else, what do you want to do? Do you want to make a render of your wall/whatever looking good, or do you want to make things for a game that are actually used in the game (and not as a pre-rendered image in a game)?