Is this a finished garage? I mean the walls & ceiling, with insulation? or is it bare beams with no insulation? There's a huge difference.
There's also a much bigger risk of ants & such getting into enclosures that are not observed as often in your normal living space, & they can kill your pets.
The only way I'd see doing this (as already mentioned) is if you enclosed & insulated part of the garage, & installed A/C, but it's still not really ideal.