If you provide adequate bedding and the temperature is comfortable enough for your pooch you should not have any problem leaving your dog in the garage overnight. Please also ensure that your dog has clean water available at all times.
It is important to consider your dogs emotional state however. You might be surprised by how your dog reacts if you move his sleeping quarters to the garage after having raised him since he was a puppy. Allow the dog some time to adjust to the new surroundings if you must leave him in the garage. Spend some time playing with the dog in the garage petting him and trying to lure him to his sleeping place with a calm reassuring voice.