I put in a gas heater a couple of years ago for working in the big barn. It really was a good move. I had to make my own gas injectors, but other than that, it was an easy installation.
Warren, I think the name of the company that supplies good gas heaters at a good price is Tek Supply. If it is too hard to find, drop me a note and I'll get you the number.
All you need to do is get either Natural ( the stuff they pipe from the road to your house ) or Propane ( the stuff you get in the bottles or tanks ). Find a good location in the garage. Put two strong 2 x 4s in the ceiling at the desired location to tie the heater to. Then, with the help of a friend or two, lift the heater into position. Cut the hole for the roof and make sure to use a double or triple wall stove pipe out the top of the garage. Then you plumb it for the gas and check the joints with soapy water.
If you get no bubbles, plug in the power and ignite the pilot ( if it doesn't have electric start ). Set the heat at 65. That should give you about 70 degrees in the work area.
