Unsold flat maintenance by Builder

Dear Sir Background context: 1) We are the Owner Association of apartment in Whitefield, Seegehalli Bangalore 2) There are 326 number of apartments of which around 28 are unsold flats of the builder 3) First possesion were given around May 2013. 4) Maintenance Started from Apr 2016 5) The maintenance is still run by the builder and not handed over to the Assocation. The owners association is running as an advisory body. 6) The current rate is Rs 2.25 per Sq Ft and without the builder contribution for unsold flats its becoming non sustainable to cover the costs. 7) Builder has proposed a 50% of maintenance on the grounds that the flats are yet to be sold. 8) Builder is not handing over as they have contruction going on and there are lot of ingfrastructre related spends they need to do before handover. Questions: 1) What are the legal provisions for unsold flat maintenance? We need to get 100% of the unsold flats maintenance from the period we have started maintenance. thanks Abhishek