Gst applicability in case of self development of residential chsl in Mumbai

residential chsl in Mumbai is going for self redevelopment. what is gst implication in terms of gst amount & point of taxation, ITC utilisation if society is urd under gst. some points are 1. existing members of society for existing carpet area 2. existing members of society for additional rera carpet area 3 new sale between society & New purchaser & what if the society is registered under gst