Dear Sir,
Hope you are doing well !!
When a developer enters into a development agreement with a Landowner, GST would become payable by the Landowner when the developer transfers possession or the rights in the constructed complex, building or civil structure, to the Landowner by entering into a conveyance deed or allotment letter.
Hence, when the Landowner receives a constructed property from the Developer in exchange for providing land, the Landowner would become liable for payment of GST.
As I see in your above mentioned case, the land holder is transferring the rights in property and in return is getting a share in revenue/area on sale of the property to be constructed.
In your case GST liability will arise on both events.
1) Sale of Rights in land by Land Owner to developer.
2) Construction Service provided by developer to Land Owner.
So, you are liable to pay GST to builder.
Thanks & Regards,
Payal Chhajed