My shed is approx 7m by 4m, cavity wall, fibreglass roof, cost was just over £5000, and that includes digger for footings, we mixed the slab with two mixers on the go, blocks, bought window and door earlier so built opening to suit, fuse box and armoured cable i sourced from freeads, wall straps timber and furings, osb and fibreglassing. At the time i didn`t insulate the cavity , wish i had now. as its a bit nippy in the winter.