Under the ROF exercise, the 577 flats comprise 173 two-room flexi units, 166 three-room units, 129 four-room units, 10 five-room units, 96 3Gen units and three executive flats. At least 95% of these will be set aside for first-timer families, and up to 5% for second-timer families. Overall, families will be given priority in the flat selection, HDB said.