I built my own 17'x25 in 2004. Slab on grade, 16" thick around the perimeter, 6" in the middle. 2"x4" framing, 5/8" Spruce ply, engineered Truses, 12' Insulated door/auto. 1 Man door, 1 typical slider window, 2 skylights, insulated and drywalled,vinyl siding/aluminum trim , gas heater...I think my bills added up to $17,000. Did most of it myself. I did pay for the pad-great price, paid a roofer to shingle it-another great price, had the heater installed that was around $2500 including running the gas line. Paid an Electrician friend to do the wiring-great price again...It helps if you can find decent tradesmen to do some of the work you can't/don't want to do.