Yup. The roofs will be very entresting as they would be one of the places with the most traffic of players. Full of tall skinny points, pools, gardens, penthouss, landing platforms, obstacles for infentry firefights.
The buildings themselfs will all have windows, elevators, room decorations, variety of lighting, plex storages (maybe with random loot).
120 block high buildings could have 5 block high rooms with like 20 floors. Random cat walks make it so that you can switch buildings without climbing to the bottem and back up.
You could rent-out structures as a server base, use it for a massive air/ground pvp spectacle, or roleplay.