I agree with Steve, I built a 12 x 14 this way and got good service from it. I blocked mine up on bricks under the 4x4s just to keep it off the dirt. Mine was of metal barn siding (to match the barn it was sitting next to), with a simple sloped metal roof (also matching the barn). Tons of storage space with about $550 in materials. Make your decking plenty strong and you won't be sorry. Good luck.