GST Liability under JDA for builder

Where a land owner enter into JDA with builder having following terms:

Total flats 100

Flats to landowner 30

Flat sold before issue of cc or first occupation 63

Unsold flats in issue of cc 7

Sale consideration of flat nearest to date of development agreement 80 lakhs

Sale consideration of flat nearest to issue of CC 100 lakhs.


Tax payable lower of a or b


a. 80 lacs*30 flats*18%× 7 flats divided by 100 flats=30.24 lacs


b. 7 flats*100 lakhs*5%= 35 lacs.


Thus GST payable by builder under RCM will be 30.24 lacs.


Is this calculation is correct ?