What foundation works best in Texas clay soil?

Texas clay expands when wet and shrinks when dry, which cracks rigid foundations and heaves things out of level. For a portable building on skids, the best answers are usually a compacted gravel pad or concrete deck blocks set on firm ground — both let the building sit level, drain well, and be re-leveled easily if the clay shifts.

A full concrete slab can work but is more expensive and, on active clay, needs proper design to avoid cracking. For most sheds and workshops, a 6-inch gravel pad that extends a bit past the building footprint gives excellent drainage and stability at a fraction of the cost.