Level floor, sloping ceiling(low in front,higher in back), sidewalls not parallel(closer together in front, wider apart in rear). You will need a good framer and drywall crew to accomplish this. Found this after web search:
http://www.hometheaterhifi.com/forum/archive/index.php/t-436.html
http://www.hometheaterhifi.com/forum/archive/index.php/t-436.html