It depends what kind of info you're after. Will the roof collapse and compromise the structural integrity of the car? No. Will the sheetmetal deform if you're not standing on a rack/structural component? Yes. While the roof is a structural component, asking if you can just stand on the roof without any context is going to get you a bunch of blank stares as you're seeing. Roof racks are designed to transfer the loads to the reinforced portions of the structure.

What exactly are you trying to do? A stock roof rack will support your weight without any adverse effect. Standing in the middle of the sheetmetal will put a nice dent in your roof.