1) it is necessary to peruse agreement to advice
2) since you are staying in Punjab and money was advanced from Punjab you can take legal proceedings from Punjab .
3) if under the agreement it is provided that in event of disputes jurisdiction would be at Patna legal proceedings will have to be taken in Patna only .
4) from facts it appears that builder has neither refunded money nor handed over flats By December 2014
5) issue legal notice to refund money with interest as per contract .
6) file summary suit under order XXXVII of CPC for recovery of money