This is the company that we went thru to have our garage built. They said it would take two days and they had it done in one. The men who came out were great and we've been really happy with the final product.
Through the HD, the "Sheds USA" company will come and build a shed right on your property. ONLY this company! You do not even have to be home! Any other sheds you have to put together yourself.
However, the "Sheds USA" sheds are larger than the measurements you desire, but they are all made of wood and have real roofs on them with shingles and such. You get to choose the wood for the walls as well as the color of the shingles. Also, a sturdy pad, or surface, is required for the shed to sit on. They are not the cheapest things, but are good, sturdy sheds.
Go to your nearest HD and look up the "At Home Services" Rep. and he will be able to tell you everything you want to know--NO obligation. Usually, they sit somewhere near the front entrance.
I had a shed (12x16) built on site (fall 2001) which was purchased through HD as well. HD delivers the materials the day before construction begins. One young guy shows up to build this the next day (different company in GA). By the end of the day everything is up including the roof. He comes back the next day to finish the trim around the windows, put in a ramp, add lofts at both ends, and shingle the roof. He also removes all the trash. The only thing left to do is paint.