Work is underway on Universal Orlando's fifth hotel — the 1,000-room, Caribbean-themed Sapphire Falls, a luxury resort. Universal has 4,200 rooms in four hotels, but executives have said they see potential for up to 15,000 rooms. Documents submitted to the Orange County comptroller's office last year show that Universal is contemplating two other hotels — one with about 400 rooms and another with about 800. The documents gave no timetable.