@mayintoronto I've learned that a roof is a giant piece of plumbing installed by a plumber (around here). It can fail like any other plumbing structure, with the usual results: water it was managing going everywhere.

This can happen if you get a massive dump of solid precipitation all at once (in our case lemon sized hail, but I suspect it would work with ice or snow), followed by a massive dump of rain in a very short period. The amounts need to be huge, but supercell storms can do that. The volume of hail on our roof looked like you could hide more than one SUV in it.

Edit: idk about other types of roof, but a corrugated steel roof can do this and not be damaged. It can "back up" like a pipe and flood everywhere, but if that exact event doesn't happen again it will never leak again. That's not going to happen with giant hail, but it can happen.

Edit again: the real trick to avoiding this is never buy a building with a roof a shape that could hold 2+ SUVs worth of anything, that's a bad shape for a roof.