First things first. Do the happy dance.

You want to be sure it does not freeze it's first winter, so be careful about the unheated garage. You can put it in a one gallon pot, but you will have to be very gentle. That is a delicate time. If you are going to put it in the garage, you could wait until it goes dormant, then repot it. I have put rooted roses outside in a protected area and covered with mulch over winter. Only lost one out of about 30. If this is your only one, then you will want to be really careful with it. The bonus of having it outside over winter is it will be acclimatized (I think that is spelled right). I have a space in my basement where I keep them now - if I am lucky enough to get some more rooted!