Consumer Redressal

Sir, I had purchased flat in 2010 , flat is at first floor in 5 floor building, 1 BHK with attached terrace ,in sale deed carpet area shown is 43 sq.m and saleable 71 sq.m ,builderverbally told 30% loading. I installed safety grills +shed at terrace ,but builder complained in pradhikaran that this structure is illegal, Pradhikaran told me that terrace is defined as open to sky and hence can not be covered. I was shocked , the terrace has slab at double height and till date builder told me it is covered and charged 70% amount ,now i read that the open to sky terrace can not be sold ,hence i felt cheated and demanded explanation from builder , please guide