IPA: /ˈruːfˌtɒp/
KK: /ˈrufˌtɑp/
The top surface of a building that covers it and protects it from weather.
They enjoyed a beautiful sunset from the rooftop of the hotel.
Rooftop → It is formed from "roof" (from Old English "hrof", meaning the top covering of a building) and "top" (from Old English "top", meaning the highest point). The word "rooftop" refers to the highest point or surface of a roof.
Think of the 'highest point' ('top') of a 'covering' ('roof') — that's what a rooftop is.
No commonly confused words.