Sold off the terrace,

Whether a builder can claim that Terrace rights cannot be sold when he is selling the apartment along with common rights in all the common areas of the building. Where it is mentioned in the law book that a builder derives a ownership right in the terrace of the building when he is selling flats which are beneath the terrace? Ultimately the builder is selling entire ownership of land below the building to all the flat owners. How can he remain owner to any portion of the building when he has sold all the flats.