Dear Sir,
GST is not required to be paid on the transfer of immovable property if the transfer is made after receiving the completion certificate.
However, the development charge is something different from the immovable property. This amount is charged by the builder for the common amenities provided by the builder and no transfer of title is involved in this case. Therefore GST will be leviable to this charge irrespective of whether the completion certificate has been given or not.
However, I would suggest you to please check your agreement with the builder to ascertain whether this term of payment of GST or other tax is included or not. That would help you out in a better way.
Trust this meets your understanding.
Thanks.