Why wouldn't you just go with a full arch quonset building? The width should accomodate a mat. So maybe the lenth could accomodate 3 mats. So for practices perfect. Portapoties outside. Showers at home. Open the garage doors at each end during good weather. Close doors during winter. Windows not required, only insulation for winter.
If all you want is a place to work out, sure. Even then, though, there are drawbacks to Quonset huts. For one thing, you wind up enclosing space which you can't use (for normal stuff) along either side due to the low clearance. You can go with a modified shape, e.g.:
... but then you wind up paying more to clear the same span (and limit your maximum possible span) because it's not as strong a shape. So one solution is to build up low walls, and then mount the quonset structure atop them. You see this sort of thing on farms, and where road equipment is stored, often using a plastic semi-cylinder.
Then you have to insulate the thing and hang lighting, both of which are difficult. Ultimately, a lot of people find it easier just to put up a pole barn. I believe the costs are roughly comparable, depending on the price of steel at a given time.
At any rate, that's a solution for just giving yourself a place to put down mats and wrestle. The plan I modeled is for a fair bit more than that. It's a self-sufficient (though minimalist) club facility, with more economic potential. You could even run small tournaments in it each weekend, if you had additional space for people to hang out.
Which brings me around to something else which has been on my mind for a long time: a permanent tournament facility. Weekend tournaments can be profitable, but they're labor-intensive (especially concessions). But if you could put together a suitable facility with, say, 8 to 10 circles, you could run tournaments (wrestling mostly, but also grappling, Judo, etc.) every weekend with far less manpower, use it for club workouts and other such during the week, and turn it into a camp facility in the summertime.