My shed has a 12v solar panel charging a 12v leisure battery to which i power 4 down lighters and a 12v converter to 300 watts. It is insulated roof, sides and underfloor with fire proofed sheeps wool.
my shed has been built totally out of reclaimed timber, even the glass came from warrington college that was broken and i cut it down to size. The timber can from a roof in rudheath and the flatroof is a left over piece of rubber epdm