Placing your shed on Pressure Treated 4 x 4's serve many purposes. Treated for in-ground contact, they provide protection from rot, decay and insects. Allowing air to pass beneath the building keeps moisture from entering. Also, if you have an area that is not level, the runners serve as beams to support the structure. Shimming under the runners makes leveling easier. Placement of your runners vary by size, and will be provided if needed, upon request.