Hi Mike,
I built a roll off roof for my obs. It is on an 8' x 8' cement slab 6" thick with a wall height of 5'. It is very easy to put together out of 2x4's which bolt to j-bolts embedded in the slab. I built the wall frames in the garage then put them in place later. The outside is T1-11 siding. I also insulated the walls and put paneling on the inside.
The roof sits on four rollers in a wood track and can easily be moved with one hand.
http://tinyurl.com/l5syaehttp://tinyurl.com/mq5rwvBrent