regarding registry of building

Yes. Once you have made some part payment before completion certificate, All payment shall be liable for GST even if part payment is made after completion certificate. so in your case, you need to comply GST on whose payment which is received after completion certificate.

Regards,

Vivek K. Tiwari

Email: vktiwari.ca @ gmail.com

Read Section 7(1) (d), schedule- II, Para 5, which says - it is out of ambit of GST only when entire consideration is received after completion certificate