I was wondering about the best way of creating a level or a room in Max ?

When creating a room I used boolean subtraction (out of curiosity) and I was pleased to see it happily loaded in WED via fbx level import.
I also created a massive room (like an aircraft hanger) but game engine was sluggish (slow)
Another observation was that when I created a window in some models, the window magically disappears when you move into the room from outside ?

Could anyone post any general wisdoms about using 3ds Max with respect to level and room design please ?

Thanks

Its been a long while since I used MAX but I recall you have to set the measurements to GStudio ratio, use blocks to creat hollow rooms or ensure your large block with windows is actually comprised of a hollow block.
Not much help but worth remebering.