When you look at the bed platform photo in the listing you will see a ladder - that is your access to the roof. We never went up there. In fact, it was a hot day when we arrived, not unusual in Palermo, and having set the aircon on, we went out for two hours and came back to stultifying heat, unchanged by the (inadequate) aircon. We left and booked a local hotel. To have a roof-room with inadequate cooling in a place where temps reach over 40c in the Summer is seriously wrong.
We’d also say that the apartment is dark and dingy - not like the photos - but that may be your thing. We never regretted our decision to move into a hotel where we could have a cool room and sleep well at night.