Take your plans to the lumber yard in your area and ask them to do a materials bid. If your useing trusses get a bid for the trusses from your local truss company(check yellow pages), figure out how many cubic yards of concrete your monolithic slab or, foundation and, slab will take call your local concrete company and, ask them how much for haveing that many yards of concrete delivered also can a concrete truck drive to your shop location if not than you will need a concrete pump truck just another call for a quote, add all these numbers together, and bingo bango bongo thats how much it will cost to build. The question your asking can only be answered by the frase "it depends on what the material costs in your area are" also how much work are you going to do yourself, framing, concrete, electrical, roofing, and anything else that you want to put in this shop footprint hope this helps.