I say - Grab yourself a decent USED table, and go for it!
I had a pro-8 Brunswick in my garage for about a year (before we moved). The garage door was insulated, so it took the edge off of extreme temps in the space. I mainly played in the evenings, after work, so didn't have to gut it out in the dead of summer during the day. I kept a floor-standing fan in one corner of the garage, and that helped a little, too.
I wouldn't suggest getting a new Diamond table and throwing it in there...but if you can find a nice used Brunswick GC or similiar, have a ball! As long as you're aware of the temp/humidity issues...and willing to sacrifice a bit in order to deal with them...there's nothing quite like having a table at your disposal whenever you want to play.
People do it all the time, and there's no reason why you shouldn't, too!