Can someone build a room on the rooftop of a 4-floor apartment building in India, even if only floors are permitted? If not, what can other residents do if someone has already built a room on the rooftop?

No, building a room on the rooftop of a 4-floor building is not allowed in India if only four floors are permitted. The other residents can file a complaint with the local municipal corporation or housing society against the unauthorized construction. The authorities can then take action to demolish the illegal structure.