Query with respect to purchase of car parking in a new flat

I am planning to purchase a flat along with stilt car parking in a stand alone G+3 building in kolkata. The building is a new construction where completion certificate has been issued by municipality. As per the approved sanction plan of the building there are altogether 6 flats- two flats in each floor and three car paring space( in the ground floor). The rest of the space in the ground floor has not been approved as a parking by the sanctioning authority. However the builder is showing the open space in the group floor as a parking area and claiming that there are altogether 6 parking spaces in the building. The space that he is offering me as a parking space is not approved as a parking lot as per sanction plan. However he is saying that he would demarcate the area in the sale deed as parking space and sell it to me. In view of the above situation request for your guidance as to the below issues 1. If I purchase the space as parking and if it is demarcated and mentioned in the sale deed will it be legally ok? 2. will I have absolute right on the garage space or rest of the flat owners can object to it As per my knowledge out of 6 flats two flats have been sold so far but registration is pending