//Why has the builder not given occupancy certificate? What could be his interest in not giving? Is there anyway we can get the Occupancy certificate as the first step?//
There must be some date by which the builder is obliged to give you occupancy certificate. If that date is there, talk about this to your builder. If it is being delayed deliberately without any reason, you send him legal notice. About his interest delaying the occupancy certificate, he may be looking for an opportunity to get additional money in one or other form.