Value on commercial building developed on sharing basis - Goods and Services Tax - GST

A developer constructed a commercial complex on development basis with the landowner with share of 50:50. But both the developer and landowner are not selling the constructed complex. After completion of the building, both the developer and landowner are leasing their share of building. In such a scenario, on what value the GST is required to be paid as there is no intention to sale the developed property in the instant case. It is clear that the rate of GST on commercial construction is 18% in terms of the Notification No.11/2017-Central Tax (Rate) as amended. Teh experts may please through light on this issue Thanks in advance.