Check out this "Shed" my father in law built. I helped built a good bit with him, but he's a much better carpenter than I.
The cool part is this storage has a 2 story room behind my trailer which is 14x10 and is used for long term storage. He also has a 6x10 utility trailer parked behind my trailer, and a a mower / 4 wheeler behind his.
My trailer is on the left, his on the right.