Think about 2 x 6's instead of 2 x 4's. My garage is 6 inch and it really helps insulate in winter and summer. Also makes it quieter in and out.
Also I have radiant heat - very efficient and no "hot air" blowing around while your trying to varnish or something. Joe Schulte had the garage built before I bought the house from him and it is deluxe and makes for a great shop.
The last time I posted a picture of a boat in it I got accused of having the boat in my living room.