12x20 modern shed plans specifications overview . foundation = 5 different foundations are included in the plans; wood skid, concrete slab, concrete pier, precast pier. floor = 2x6 floor joists with 3/4" floor sheathing. walls = 2x4 framing at 16" on center with a double top plate and the lower shed wall height is 7'-7". 12x20 modern shed plans specifications overview . foundation: 2 foundations are included in the plans; wood skid and concrete slab. floor: 2x6 floor joists with 3/4" floor sheathing. walls: 2x4 framing at 16" on center, 7/16" o.s.b. sheeting that allows most sidings to be applied.the lower shed wall height is 7'-7" door: the specified door is a 9'x8' full glass vinyl door with one panel operable.. Click now to buy our 12x20 modern shed plan. plans include materials list and all needed instructions. lean to roof design..