if a flier taxis another person next to a building can that taxi drop them off on top of the building even though they are not on the building too?

A taxi must drop his "fare" off on the same elevation that the taxi ends his movement on.

To be more specific, they must drop off the other character in an adjacent square. In your case, they are not adjacent to the elevated terrain and so can't put them on the roof.

cool that came up last night and my friend thought I was making it up.