Query on Apartments Association formation

I would to take an initiative to form association for our apartments, I don't have the complete owners list but we know hardly 150 + owners only out of 380 apartments and Handover mail have been received most of owners and we yet confirm the Handover/ possession.. The builder is not completed most of the items as they promised and pushing customers to confirm NOC ASAP so my question can we form our association with 150+ customers NOW and approach builder to resolve our issues through welfare ??