Jason, I lived in Texas for 4 years and understand why you need a cooled garage there! Here it is the opposite, need a heated garage - so I added a gas heater.
The way my wife agreed to it was that I added living space above the garage (more square footage to the house). We ripped the dormer off the back and made a door from the room upstairs into a new finished area. But, unlike Steve, I cant stack cars - so, that part I had to give up. However, on the other side I did not photograph is room for two more cars.
I am enjoying making it my "own little hideout". I have threatened to put a lazy boy in the garage. There is already a stereo system, phone and fridge out there (no TV). I have heard of guys actually falling asleep while working under their cars...I could definitely see that happening here.
Casey