Open terrace rights

Sir, Recently we purchased a property which is a joint venture. The land owner is a single person and the builder is proprietary concern. Jv is not registered. In jv the owner and builder has 50 - 50 share. He has alloted 3 flats to owner one in ground floor, and 2 in second floor. The 1st floor consists 3 flats which builder share he sold to different buyers. As per plan aproval there is a pocket terrance in second floor. In that open terrace the builder constructs one additional room to owner which not mentioned in approval. In jv they said that the open terrace in 2nd floor has right to be enjoyed by all flat owners but it was overwriten as enjoyed only by land owner. The owner also sold one flat in second floor. Now he has only 2 shares. My questions are the deviation of plan approval ie., additional construction is valid. The unregistered joint venture is a valid document in court of law. They mentioned in jv as the right of enjoyment is solely to land owner is valid. If it is valid the owner has to construct any building in future. If he sells that second floor property to other person the right of open terrace in that floor is also transferred.