Construction and terrace rights

Dear sir, madam I have recently purchased a three BHK flat in Jaipur The building is approximately 6/7 years old I have purchased it from the builder , and I am the first owner My flat is on the top 4 th floor and there are two flats on each floor , the other top floor flat top is recently purchased by somebody else There is a common terrace above my flat Recently I come to know that the builder is trying to sell the whole terrace to a party And the party plans to make two flats and penthouse above it and extending the lift to sixth floor There are total eight flats presently in our building and there is no more parking space Not even the the lift goes above the fourth floor As discussed with builder he says previously there was permission to built only four floor And know he has the permission to built one more floor I request you to please guide on the issue That is builder entitled to sell the terrace Or he is entitled to built a flat and sell afterwards In that case the terrace will be common again Our building has not a registered society