Pierre, we have 5ft x 2ft piers under the beams. The office area up front has plastic. The shop area does not. Reason for that is the offices will have floor covering. The shop will not. The footings are 18"x 18" on the sides and the back. The front footing is 18" x 24" with 6 piers in front for the parapet wall.
I was pretty picky on the saw cutting and requested that the cuts be what I wanted. The concrete contractor agreed and did a good job.
I think in all there is 450 yards of concrete in the footings, piers and slab. Shop part is 6" and office part is 4" with spot footings and piers where the load bearing portion of the walls are for the trusses under the mezzanine.
I have been around countless buildings with dozens of concrete contractors. i have been around excellent and horrible concrete pours. I have learned what made the pour bad and tried to make sure that did not happen here. I think the concrete turned out ok, not flawless but not real far from it. It will be easily functional for what we need. Total costs of concrete slab was $57,000. Not too bad.