I built one at my parents house back in 00' with some simple figuring and planning.
10x12(wish I had gone much bigger)
I put it on concrete pads = no building permitt 14" elevated.
The floor is framed 4x4's and 2x4's, and decked with sealed 2x6's
I set the walls just like a house 16" stud spacing. enclosed it with that 20 year siding type stuff from home depot.
Built trusses for the roof = rafter storage
I boarded, tar papered, flashed, and shingled the roof, even added a ridge vent

Then painted it. It has survived two huricanes now, doesn't leak a drop.
Built it myself and am damn proud of it for using no plans.
total cost if I remember right with shelving and all was around $700
Only place I really saved was the 2x6's which I already had
Can't touch a pre-engineered shed of that integrity for that price. I built it over two weekends and a few afternoons.