Flat handed over without amenities like RO plant,swim pool etc

In Chennai, the builder agreed to hand over possession by 31.12.12 through agreement.The project carries amenities like RO plant,swimming pool, club house, Gym etc. Flat handed over through a letter in Sep'15 without the specified amenities. Even till now the amenities not completed and project not handed over. We have paid the cost including amenities but builder delays. The agreement say the purchaser has to pay 18% interest for delay payment.We have paid all the payments promptly. Further during rains since the flat is in topmost floor, roof is leaking like a hut and water seeping in the walls. The following questions 1. From 01.3.12 to till date can seek interest on on delay in construction or Sep'15 though no amenity 2. Can we sue the builder on the grounds that the flat without amenities is incomplete without amenities as agreed. 3. Upto which date interest can be claimed and what could be the compensation for the sub-standard construction of roof leakage for which the buyer has to suffer permanantly 4. What other course of legal actions can be taken and the suitable forum