I put up a 24x26' (12' high at peak) covered tubular arch building bought from Tek Supply last spring. Good quality componants and pretty heavy guage and tear resistant material. Cost about $2100.
I poured a 6" rebar reinforced slab for base (over a few " of crushed stone) w/2' ground screws under the slab at each end of the rafters for anchoring them and 2 4x4 timbers at each end for stiffening against wind loads.
2 reasons; (1) it gets pretty windy here so you really want the building well anchored and the ends able to stand up to pretty strong wind loads and (2) I keep my attachments on dollys and that won't work on a gravel or crushed stone base.
I am pretty happy w/it and it seems pretty stable so far. I ran 100amp service out to it via underground conduit, for lights, and my air compressor, welder and plasma cutter. Doesn't seem quite "temporary", does it? /forums/images/graemlins/grin.gif But that's how it started, anyways.
SWMBO claims that it is "the ugliest thing in the United States, and possibly the Universe" but that just shows that non-tractor owners have no aesthetic taste at all. /forums/images/graemlins/wink.gif
If you decide to go w/ covered tubular arch construction, I have some tips on a couple of useful modifications that I'll be glad to share, by PM or post.