Not a builder by trade but if it I were figuring for myself here's what I'd look at. Mind you though that without alot more information what I'm thinking would be nothing more than a wild a$$ed guess, at best...
First are the 32 sheets of galvanized just for the roof, or are some used for sides too? That said, given the length, and that there are other painted sheets, I'd have to assume they were for the roof. If that's the case then half the number to 16 to start with. Then take the width of each piece, minus twice the overlap distance (for example 2 inches for each piece, or 4 inches per joint) and the overhang desired on each end, and multiply the result by 16. This should give you a rough idea on the length of the building.
Beyond that I don't know how you'd tell the width without more info. That said, a wild guess, it stands to reason that it would have a maximum ridge height of the longest painted piece, or 13'1" a side wall height of 12'1". The problem is that doesn't leave much of a pitch so as much as it seems to make sense, it really doesn't.
Basically, beyond a rough length, and a guess on a width based on calculating the span of two fifteen foot pieces set at the pitch you want to put them on, there's really no way to figure anything accuracy. I don't know about you, but I personally wouldn't feel comfortable spending money on pouring and finishing a pad to set a building on unless I knew exactly what size it was going to be. My suggestion would be to figure out who the mfg was, if it was a manufactured building, and call them. You never know, in 5 years there could be pieces missing that make the whole thing nothing more than a pile usless steel, and you'd never know it.