I am building an auto body shop 60x80 and need to bring the pad up about 3'. I am planning on bringing in all the fill and compacting and wondered what everyones thoughts were on the cheapest/best foundation. It obviously will have a concrete slab and it steps down 2' at 25' in. I am more concerned as to ideas with retaining walls, piers, grade beams, and footers. Any advice is appreciated and thanks in advance.