Generally, if a new home is in a subdivision, the builder typically rolls the HST into the purchase price and then gives the Buyer credit for the rebate. The builder then applies for the rebate directly. In the case of Multi-family projects, generally the HST is included in the purchase price of the unit, the new Buyer/owner has to claim the rebate themselves.
If the propert owner is an "owner-builder" designate or has hired someone to build the home for them, please contact your nearest Canada Revenue Agency office through 1-800-959-8287. All forms are available at: www.cra.gc.ca