Problems with Booleans and Rendering

I have been working on a model of Kakariko Village from Ocarina of Time and I have run into a few small problems. I want to put recessed doors in the buildings and I wanted to do that with booleans. I have had some experience with 3ds Max’s boolean function but when I tried to use them in Blender I was totally confused. What I don’t get is how would I use a cube to add geometry to a model with booleans. I also have been having a few problems with rendering namely when I try to render it just gives me a gray grid rather than showing my model.

Boolean in blender is horrible. My suggestion, use edge loops to do cut-outs.

I’d agree. Forget booleans, they don’t work very well at all and will give a horrible mess that you’ll want to clean up afterwards. Just use basic edge loops and extrusions, quick, clean, simple.
As for the rendering question, too little to go on to give an answer.