You might try the Heating and A/C forum on this site.
In the mean time, PEX layout is easy and probably pretty quick to do on a 24 x 32. The layout depends much on your heat loss, how much comfort you want (take the chill off or just like the inside of your house), and layout of the doors and windows (specially the large garage door).
There are some "rules of thumb", but that doesn't mean your good to go or that other methods won't work. See below.
1) Vapor barrier under the slab
2) Insulation around the perimeter and under the slab
3) Limit loops to a maximum 300 feet on half inch pipe
4) It's common to see 1/2" pipe placed on 12" centers
That's a place to start.
Best of luck,
Reflex
