So I figured out what to do with the roof. I used some kinda lame barricade that comes in the Battlefield Accessories Set. I had 3 of them and they fit very nicely and then I added some card stock shingles. Tada a roof!
The rubble looks much better and not as uneven as I feared. The process is smash some plaster bricks with a hammer, add in some dirt and scatter junk and used weapons.