A word of warning though, unoccupieable buildings will have units placed inside of them, and not on the roof.
This really screws with the player controlled unit since you cannot move and the graphics are just weird. :-\
AI won't have a problem, they mysteriously can walk through walls, so they won't get stuck like you.
That script Grim Monkey put up works great for anything except tanks.
Last thing I gotta say is that the building postion option in waypoints works well at times and screws up too. An AI may be facing a wall instead of a window, or might not even go into the building at all.
Okay I'm done now. :cheers: