24 C.F.R. § 8.29

Any housing units newly constructed or rehabilitated for purchase or single family (including semi-attached and attached) units to be constructed or rehabilitated in a program or activity receiving Federal financial assistance shall be made accessible upon request of the prospective buyer if the nature of the handicap of an expected occupant so requires. In such case, the buyer shall consult with the seller or builder/sponsor regarding the specific design features to be provided. If accessibility features selected at the option of the homebuyer are ones covered by the standards prescribed by § 8.32, those features shall comply with the standards prescribed in § 8.32. The buyer shall be permitted to depart from particular specifications of these standards in order to accommodate his or her specific handicap. The cost of making a facility accessible under this paragraph may be included in the mortgage amount within the allowable mortgage limits, where applicable. To the extent such costs exceed allowable mortgage limits, they may be passed on to the prospective homebuyer, subject to maximum sales price limitations (see 24 CFR 235.320.)