You could even be able to place some furniture on top of them, or just have them come with pre-designed tables, chairs, and whatnot. In order to access the roof of your house, instead of trying to jump from other houses or mountains (if available close to your location), you could just have a clickable light (in and out of the house) which teleports you to the top. Not fancy, but works. Otherwise, make furniture that lets us climb up, or change the house walls to be climbable somehow to the top, but really! Having this option would create a brand new way to enjoy the amazing panoramas of the housing areas, imagine seeing your neighbors on their rooftop 3 plots away and waving to them, that's just beautiful, it would give a whole new experience for housing. Mid sized and larg sized plots have soooooo much wasted space up there, and there are so manu possibilities to model interesting rooftops.

http://onebigphoto.com/elegant-rooftop-room-new-york/