Purchase of a resale under construction property

Hi,nI am looking to purchase a resale under construction property which is nearing completion (in another 6months). The seller has completed full payment to the builder and took possession of the flat. Even in other flats I can see people have started residing (electricity and water connection is there).Since, couple of towers have final work left and parking area is not completed.. there is no OC, CC issued - due to be completed in next 6months.Without OC/CC there is no sale deed between seller and the builder, only agreement of sale is thereCan I get some guidance on how should I proceed with this transaction? Is an agreement of sale with the seller + NOC from builder sufficient? How will I ensure when project is completed builder completes sale deed to my name?