Our installed sheds are built on 4×4 pressure-treated runners (aka skids), so you can install a shed directly on the ground without needing a foundation. Unless required by local building codes, a concrete foundation is not required. Check your local municipality for details.
DIY shed kits will need runners (two to four 4×4 pieces of lumber, depending on your shed size) or a concrete slab foundation (not included). Exact measurements and material quantities are included in the instructions.