Garage Insulation
 

I'm looking to finish insulating my garage. it is attached to the house so one wall is already insulated. it has covered walls that are drywalled. My question is, would I be ok to insulate the side walls and the wall that the roll-up door is on and not insulate my ceiling, or would it be recommended to do the ceiling? I store my Genesis in the winter and dont drive it so I was thinking insulating the garage would be good for the car when it gets cold out. There is no heating or cooling going to it right now. I probably would do some type of spray in insulation so I dont have to remove the drywall completely.