Yeah this looks super unstable in the long run, and they look vulnerable to heat / heavy rain in a way that will interfere with their life expectancy even if they stay in place on the roof.

Maybe it’s temporary, or maybe I’m wrong and she knows what she is doing. Maybe the cords that are laid along the roof are anchoring the whole thing in place somehow. Maybe that little balcony below is already chocked up full with plants, and she’s putting the surplus up here and staying alive is their problem.