Wow that's crazy that structure caught enough wind to shift and fall over; I'd imagine it would have been heavy enough to stay planted, but perhaps it was just some crazy wind you got....but would likely happen again if you don't remedy it
Looks like it fell on its back, right? I'd guess it happened because of the amount of roof overhang on the high-side, the roof's pitch, the very skinny footprint vs height vs roof size, lack of wind breaks in your pasture, etc - all contributed to this event
I know before you said in your build thread you don't want to have any concrete foundations on this project. IMO setting 4 corners in concrete isn't very intrusive and easily removable in the future. Heck, even a few of those solid-cast concrete piers are likely better than hollow cinder block - significantly more weight and have anchor straps to fasten the structure to them. Another alternative is to drive some U-Channel/sign-post into the ground at each corner and lag bolt the structure to those stakes.
If you were considering slight design changes to lessen the amount of air lift underneath the roof, my gut says add more ventilation space underneath that low-side so there's more "flow" through the structure so less wind catches under the roof. Adding that air gap would also make the roof less pitched and less sail-like, which should help in multiple ways.
Bummer on that nice new roof taking a beating though, stuff happens.
