Common things that will add to the $ per sq. ft. cost of a concrete slab:
1. THICKER EDGES (from 12" - 2') ADD $ to $ PER SQUARE FOOT
2. VAPOR BARRIER UNDER SLAB - ADD $.50 PER SQUARE FOOT
3. 2 INCH STYROFOAM UNDER SLAB - ADD $ PER SQUARE FOOT
4. WIRE MESH INSTEAD OF FIBERMESH - ADD $.35 PER SQUARE FOOT
5. PUMP TRUCK IF CONCRETE TRUCK CAN'T REACH - ADD $ TO THE TOTAL PRICE (approximate)
If your concrete slab is only 4" thick instead of 6" that will reduce the total slab cost by $.50 cents per square foot to $ per sq. ft.
Any dirt work and grading of the sub-base would be an extra cost as would adding radiant heat to the concrete slab .