In the game right now roofs are very safe places because we lack enemies that spawn there or can get up there. I think that creatures with the leap ability should be able to jump up one Z-level to follow the player onto the roof of buildings. This would make roof not as safe as they used to be without having to add entirely new enemy types. This would also make sense since enemies with the leap ability are supposed to be agile and nimble so jumping/climbing onto a roof would make perfect sense for them.
If we also where to make them spawn on roofs than this would make them a danger during night raids given that some of them have good night sight and could easily spot the player from the roof since you can’t hide behind anything. This would give the impression of them setting ambushes by waiting on roof tops and striking when seeing a survivor while also using the roofs as vantage points to spot prey.
Currently in the game we lack a enemy type that spawns on rooftops and