Do a search for hot water in floor heat.  It will take a while to sort through them all.  Here is a quick summary of what you'll find:

1) INSULATE! Remember, insulation is buying the next 40 years energy at today's prices  Put insulation under the slabs well as insulate the edges

That came from the Radiant Company http://www.radiantcompany.com/details/methods/grade/

There is some science and maybe a little bit of an art to placing the pex.  You want to plan for your use.  Zones, multiple runs, etc all need planned.  here is some good info at http://www.radiantec.com/pdf/Radiant_Heating_Tubing_Layout.pdf but it isn't geared toward the shop as much as a house.

Delivering LP to farms over the years I found there was nothing like a shop with a properly designed and installed system.  And NOTHING like one put in wrong.