Metal shed kits are the most economical way to go for a truly cheap storage shed. But if you don’t already have a suitable concrete slab you will need to build a wood floor.
1/2” OSB (organized strand board) is suitable in most cases, but you can use 3/4” CDX plywood for an even sturdier floor. Placing 2×4 floor joists 16 inch on center will make a stronger floor than 24 inch on center.
If you live in a wet environment you might want to use treated lumber for your new floor. But this is less necessary of you make a proper foundation that eliminates ground contact and provides sufficient ventilation.
In either case you should use pressure treated lumber for any wood that is within 4 inches of the ground because termites can build exploratory tunnels this high. And if they contact any untreated wood they will have a super hiway into your shed floor.
A combination of concrete blocks and pressure treated skids will provide a sufficient termite barrier in most cases.
- To build your floor lay two pressure treated 4×4 runners parallel on the ground, spaced about 5 ft apart.
- If your site is not level you can place concrete block underneath the skids every 4 ft or less and use wood shims between the blocks and skids to level the shed.
- Now lay your floor joists across the runners.
- Mark your outside (band) boards for 16 inch or 24 inch on center, then nail them to the floor joists with two 16d nails.
- Square the frame by pulling a tape measure diagonally across the floor in both directions and shifting the floor until the measurements are equal.
- Nail the floor joists to the 4×4 runner with 16d nails.
- Now you can level the frame by using wood shims between the concrete blocks and skids.
- Recheck your square and level until both are correct.
- Lay your floor sheeting on and nail it with 8d nails every 6 inches along the edges.
- Then snap a chalk line along the centers of the floor joists and nail the interior of the floor with 8d nails every 12 inches.
Your floor is now ready for your metal shed. Follow manufacturers instructions for shed assembly and instructions to attach it to your new floor.
You can lay a bead of caulk underneath the wall as the last step before you attach it to the floor to make it a little bit more waterproof.