Here is a link to some FREE shed plans you can use to build a shed!
We built our combination shed on a 4-in.-thick concrete slab, which makes an extremely durable and weatherproof floor. You could also construct a wood-frame floor using pressure-treated 2 x 6 lumber and a plywood deck, and support the assembly on solid concrete blocks or pressure-treated 6 x 6 skids. If you go with the slab, it’s a good idea to hire an excavator and mason to have the job done right. Place anchor bolts in the concrete for securing the walls, taking care to avoid vertical frame locations and wall openings.