While I don't want to go the full B&Q cardboard route, I'm comfortable enough assembling a basic small shed.
I am now shedless but if I was to buy another then I'd buy a cheap one, rip of the roof felt and instalI Firestone EPDM with a good overlap. Or, make one out of pallets and do the same.

http://theselfsufficientliving.com/10-free-plans-to-build-a-shed-from-recycle-pallet/