1)if construction is un authorised flat can be demolished by muncipal corporation
2) you have to apply for regularisation of flat by paying penalty if permitted by CDMA
3) apply under Section 113C of the Tamil Nadu Town and Country Planning Act, 1971.
4) The completed applications should be accompanied with building plans, ownership details, earlier approved plans if any, patta and property tax working sheet detailing the number of floors and built up area of the building which was in existence on or before July 1, 2007