building pole barns in the sky

I'll add a +1 on building it as big as possible. You just about can't overdo it, and it will fill up faster than you can believe. Mine is 30x40 but has a 10' wide room (fully insulated, heated, with water and drainage) all the way down one of the long sides, reducing the actual shop floor space to 20x40. I'd love to have another 20' or so. Going with tall walls is a very cheap way to gain space. My walls are 12' at the eaves, and I'm planning to add a 4-post lift so I can work under my car, and also store a second vehicle in there by stacking them. Don't forget the beer fridge, sound system, TV, and other creature comforts!

As far as pricing goes, in my part of the world (Pacific Northwest), a pole barn means pressure-treated 6x6 or 8x8 poles, with wood purlins and sheet metal walls/roof. My buddy did a gorgeous 36x48 shop with 13' walls for about $18K, shell only. If money was a consideration, I'd build a large shell and finish it off as additional funding allows.