I dunno if this has been suggested, but I think it may be neat if some building had actual attics. In those attics would be windows that led to the roof. I drew a terrible diagram, but its just an example.
I dont know exactly what the roof would look like, so I didnt put anything. But the basic idea is that you can see other roofs from the one youre standing on. Zombies obviously wouldnt be able to get you while youre on a roof, and maybe being on one would fill out your map farther? Also walking towards the edge of a roof would give you a Y/N prompt for jumping off or not. This doesnt seem too useful, but what if there was some sort of craftable item, like a grappling hook? Having Parkour Expert may make it more likely that getting from roof to roof would actually work.
Intensity intensifies
Grappling hooks already exist in-game. The reason we don’t encourage this sort of thing is because then folks will want to drop stuff off the roof and hordes will pile up and eventually human-stairway and/or hunter-climb, etc onto the roof.
Basically, you’ve hit the interlevel-interaction problem.