Legality of parking space in sale deed

Respected Lawyers, I am purchasing a property in Navi Mumbai, Maharashtra in a newly developed CIDCO node. The builder has asked me to pay 2.5L for a parking space which he says he will allot me officially during society formation. I understand that builder can not sell parking spaces as they fall under common areas & not in "Flat". There are only 35% parking slots available & I do require a parking area for my car. 1. Is it true that if parking area is mentioned in schedule C of sale deed then it is legally assigned to me permanently? (Ref: i.e. Society can not change the allotment to other members by a lottery. 2. Can builder include parking space in sale deed as of 2016? 3. If I trust the builder & pay him 2.5L what precautions should I take to recover this amount in case of break of trust in future? e.g. paying by cheque & taking acknowledgement receipt. If such receipt is taken then what is the legality of it in court? 4.Any other suggestions for someone like me who has no option but to pay the builder for a parking slot & avoid future legal implications after the society formation? Thanks in advance.