Build-To-Order (BTO) flats are HDB flats that are built based on the percentage of bookings of apartments. If more than 60% of the apartments in the BTO flats have been booked, then construction will begin right away. Otherwise, construction won’t push through. Because there needs to be a demand first prior to this type of real estate property being constructed, there is a particular wait time for BTO flats. Once HDB receives the sufficient number of qualified applicants, they will then have to wait another three to four years before the building is even constructed.