Any idea how to figure how much water can be collected per inch of rainfall from a Quonset hut shaped building? Would I just use the foundation size for area?

Yes, use the foundation size only… theoretical water collection is about .62 gallon of water per square foot of collection area, per inch of rain… but as a rule of thumb, I use .5 gallon of water because of evaporation, and other losses… I am familiar with Quonset huts, but installing rain gutters on them might be a challenge… the ones I saw had the corrugated sheets running horizontal, and not vertical… and corrugated metal sheets might be difficult to gutter unless one did it at the bottom of the hut’s sides.

I’ve seen some spacers or blocking or whatever you want to call ’em that were flat on one side and matched the corrugated metal on the other side and are put at the edge of the roof to keep bugs and stuff from crawling up there. They’re foam (generally) and completely block the space between the underside of the roof edge and the fascia board on a conventional metal roof. You might be able to adapt them or copy the shape to use as an adapter between the roof and the straight side of a gutter. That’s maybe not the easiest thing to visualize – so if you can’t let me know and I’ll do a quick pencil sketch and scan it and send it on to you.

I was kind of thinking along those lines too. If I put the gutters at the bottom, then I’d need some sort of sump at the end with a pump at the bottom to pump it into a tank. There are a couple of problems with this arrangement though. Around here the sand blows a lot and would get into the gutters and sump. Is that a problem, or can I just filter out the mud when the pump picks it up? The other problem is the slope of the gutters. How much slope should I have. The building is around 200 feet long, so it would get pretty deep if the slope was very much at all.

I know what you’re talking about. It’s an option, but thought I’d try slipping a strip of bent flashing a couple inches under the bottom edge of the corrugated tin with the bent part sticking out like a slightly open angled “L” to guide the water into the gutter. I might just put the bottom part of the flashing over the inner edge of the gutter.

Good idea. Generally, 1/8″ per foot is considered to be a good drop for gutters. That’d be 12.5″/100′ or 25″ for the full length of the building. Might be easier to slope to the middle and collect from there.