GST exemption for development rights, FSI and lease premiums with reverse charge on unbooked residential units at completion. Exemption for GST on supply of TDR, FSI and upfront long term lease premiums to promoters for construction of residential apartments is provided by apportioning GST on those inputs to the residential carpet area share of the project; the apportioned residential share is nil rated. Promoters must pay tax on the proportion attributable to residential apartments that remain un booked on issuance of completion certificate or first occupation under reverse charge, calculated by apportioning to un booked carpet area, subject to prescribed caps; tax liability arises on completion or first occupation. Valuation rules and definitions for apartment, promoter, project, carpet area and related terms are specified.