immovable property is out of GST as it is out from definition of goods. also check schedule III which says supply of land and building (Except when part consideration recieved before completion of construction & issuance of OC) is neither supply of goods nor service.
As per Para 5 of SCHEDULE III of the CGST Act 2017, Sale of LAND and Sale of BUILDING ( subject to clause b of Para 5 of SCHEDULE II ) is neither treated as a SUPPLY OF GOODS OR SUPPLY OF SERVICES.
Hence GST not applicable in sale of commercial building.
TAXABLE EVENT under GST : SUPPLY OF GOODS OR SUPPLY OF SERVICES OR BOTH.
Since Sale of Land and Building is neither treated as Supply of Goods or Services, no GST applicable.
Yes if the whole consideration ,is received after the completion certificate , then it's not cover under Supply , but if any amount received before completion certificate , it's considered as supply & GST attracts