How to file case in consumer court in regards to delay in possession

I am part of a registered buyers association for a under construction property in Navi Mumbai having some 80 members. Each of us have bought flats at different parts of time from the builder of the property starting from 2011 to 2014. Each of our sale agreement is registered and date of possession promised to us was different as per our agreement. My date of possession as per my registered agreement was June 2014 while the last date of possession as per another agreement is December 2015.However, none of us have got the possession of flats