1) file RTI with muncipal corporation and obtain copy of parking layout sanctioned by muncipal corporation
2) it would mention stilt car parking slot along with flat numbers
3) issue legal notice to builder to rectify parking list given to socirty
4) if he fails to do so move consumer forum against builder and seek refund of money paid by you for parking with interest
5) please note that builder cannot sell car parking slots . it forms part of common areas of society for benefit of all members