I used my 10x10 dog kennel so to span across I used a 4x4x12' then cut small pieces for a little more pitch then 2x6x12' for rafters so it has a 1ft overhang all around to keep the drips out, got it at homedepot went with solar gray corrugated roofing it only allows 35 percent of UV I like it but it was like 35 bucks a sheet for the 12ft ones, I found 12ft galvanized roofing at Lowe's for 21 bucks a sheet if I had trees around I think I would have used the metal just for the durability, the stuff I used is very easy to work with.