I've actually been able to do this, at least with civilians. Start your unit outside the house, then give him a move waypoint on the house. Make sure it says "HOUSE" as you put down the waypoint. Then in the waypoint box, there's a new drop window that says HOUSE POSITION, and there are numbers (usually around 8-10) that indicate different positions in the house. You'll have to check where he goes for each number, but a few of the numbers always make him go somewhere to the upper floor (if there are any) and he'll stay there. I think you can do it with some other waypoint types too, like Sentry or something. I've put snipers in buildings like that too, but that have a bad habit of not firing until very late. Anyway, that should work. I hope that's clear enough. Post again if you have problems. Later.