Last Winter I rigged up a series of racks to store my firewood in, and covered them with a giant tarp. While this did work, dealing with the tarp became an enormous pain in the ass. Last Winter, I resolved to build a woodshed. I did just that.
My property is sloped, which is great for drainage, but a pain in the ass for building things. I dug three trenches and filled them with 1" minus gravel. After that I built a level floor on a series of piers.
The next step was to build a floor of 3/4" plywood.
I built a frame from 4"X4"s on which to construct a roof.
A roof was then constructed from 2'X6's and 1/2 inch plywood.
I installed a standard tarpaper and shingle roof.
After adding some fence planks and staining it, I have a shed.