Interesting question. From what I gathered from this nature study on that, it seems that solar farms can increase ambient temperature compared to an area with some vegetation, which may be due to the panel preventing the ground from irradiating heat as effectively (by like, bouncing it off the back of the panel) and removing the vegetation that cools the area from evaporation.

But I think on a rooftop that may not have as much thermal mass as the ground, it may not have that effect, and overall should lessen the cooling needs of a building somewhat due to the shade the panels provide. Panels also don't get quite as hot as an unshielded roof, since they do reflect some infrared energy despite their dark color.

tl:dr, probably not much or at all since they're on a rooftop, and if it does, it could probably be mitigated by planting more trees and vegetation in the city (which can drop temps up to 8 degrees). But that's mostly an educated guess.