The allotment of parking space shall be done by the society after it is formed. The builder cannot do this, he has to handover possession of the flats to its owner and the master plan to the association. Even if the builder is allotting the parking space, the association after formation can re-allot the same as per the rules meant for this purpose.
Your doubts and grievances on the builder's act can be clarified with him in person and if you dont get proper response, you may issue a legal notice venting out your grievance and demand reply as well as relief from the builder quoting relevant rules.
You can consult a local lawyer in this regard and initiate proper legal action as and when necessary.