Eric,
I woiuld like to back-up what Wendell Avery said. You will NOT regret building this structure. I too had my Whaler sitting out, covered up with three big blue tarps, over a 2x4 super structure, to shed snow and weather!
My shop started out as a 24'x24' staructure. I laid it out on 1/4" graph paper, and had a cutout, similar to what an interior decorator uses to plan a furniture layout in a room, of every boat, auto, toy I owed at the time.
When it didn't all fit into the 24x24 size, I opened it up to 32' X 32'. The day we set up to dig the footing, my buddy pulled the back two stakes and moved it back 6'! He said that I'd never be sorry with a bigger shop. Whenever he comes over, we go out for a beer and his "FREE" lunch. I cannot thank him enough for doing that.
Also Eric, make sure that you get a good air compressor for your shop/carving area. an 80 gallon, two stage, with cast iron cylinders. You will not be disappointed. Air tools are cheap and the longer you use them, the cooler they get. Also invest in a ceiling gas heater if you have a smaller area you want to heat. I will post pics of my air set-up later this week.
Art