I just built a similar booth to Centerlines. I used 2x4's for the frame. It's 20' x 12'. I used heavy weight plastic with all the lights outside the booth. So far I've painted one car in it and it worked pretty well. I'll definately add more lights for the next car (sometime this week); I don't think you can have too many lights. The plastic got a bit covered with overspray, but nothing too bad. I used two box fans, they seemed to work pretty well. The back door is a single piece of plastic with a 12' piece of wood at the bottom. When I was spraying I had the door rolled up about two feet off the ground. The exhaust was through this 2 feet. Seemed to work pretty well.
81 Grand Prix, 355, 700r4, 8.5" 4.10
64 Oldsmobile Jetstar, all original