Are OC & CC mandatory in Bangalore?

We are planning to buy an apartment in Bangalore. All other documents are correct but it doesn't have OC & CC. The builders say as they've built one floor extra from the sanction plan , it would cost them high to obtain those documents from BBMP and the apartment pricing would increase pretty much than the present. That's the reason for not getting those certificates and most of the apartments in Bangalore don't have them they say. They say they'll be giving a OC from builders' end. So, is it OK to buy it..?? Will there be any legal issue further or during resale. Need a honest advice ASAP from a practitioner in Bangalore. TIA.