That is the system I am currently installing in my shop. I am just now to the point of pouring the concrete.
I put 8 inches of sand base down, and compacted it, then two layers of poly vapor barrier. I topped that with 5 inches of hi-density foam, and laid out the re-bar.
Then following directions on the net I got the right kind of PEX tubing and laid it out so that all around the perimeter the lines are 6 inches apart, and are one foot apart everywhere else. I used half-inch ID pex, and no one line exceeds 150 ft. in length. (a lot of lines for my 40 X 60 shop!) Then I added an inch of hi-density foam between the actual floor and the foundation walls (Why try to heat the foundation?) and between the "inside" floor and the "outside driveway" (again, why have heat transfer to the driveway - its the shop you are heating, not the whole world!)
Now my next steps (this week) will be filling the lines with anti-freeze and pressure-testing them (individually) to 100 psi to check for any leaks. Then cap them all off (leaving them full of anti-freeze) and pour the concrete.
Last step will be installing manifolds to distribute heated fluids and collect the cooler returning fluids, the add in a boiler/heater whatever and a pump to keep things circulating, all controlled by thermostats in each of the three zones.
If you are going to do the work yourself, the best instructions I have ever found are at:
(I have no affiliation with this company)
a great layout assistance for in floor-heat tubing runs can be found at:
(again, I have no affiliation with this organization, either!)
Hope this helps!