RE: Anyone converted a tool shed into a hobby room?
No, but my wife told me to consider converting the dog house a few times
My neighbor has a shed converted into a shop and it is nice. He has it set up to take with him if he moves as well and can run off a generator and propane if he wants. It cost him about $2500.00. He has to keep it mobile to avoid taxes and additional permits. Not having a foundation will limit the effectivness of heating and cooling and will allow critters access to live under the shed.
Anyway, whatever you do, check your building codes. Our city requires a permit if you are running electrical to a shed and then they will inspect it. Which is smart, you don't want to be running an AC, heater, refridgerator, compressor, TV, stereo, and microwave off a 10 GA extension cord attached to a 15 amp breaker that also services your bathroom. The wife may get a little upset while she is sitting on the pot, drying her hair, and the lights go off and she starts smelling smoke because you turned on your compressor. Same goes with adding electrical services for AC and heat to your garage, have a professional check out your set up and give you some suggestions before starting. Adding the area of a garrage may put on more work than your current heating and cooling system may allow, so you may need options of a seperate units for the garage or a larger system for the house.
Scott