cool, the possibilities are endless. i'm going to write up an addendum on how to do round rooms and the walls you have that are slightly off.
i can tell you how to do that. as you know holding the shift key will add to the selection. you also know that holding the ctrl key subtracts from the selection.
so that's what you do. hold the ctrl key and select into the room. that part will be subtracted out and you will have the wall selections