1) thrid floor owner cannot construct on terrace without the consent of other co owners
2) the reason being terrace forms part of the common area .
3)In the case of Bihari Lal Jalan vs DDA ( Civil Writ No. 2034 of 1992) the High Court of Delhi vide judgment dated 18th February, 2003 has held that the terrace is a common portion and does not belong to the top floor owner. The Court has held as under:
“ Common areas or common portions must remain common to all the allottees and can not be grabbed by any particular allottee or group of allottees for their exclusive use. In so far as exclusive use of the top portions by the top floor owners is concerned, we feel that the top terrace is a common portion as described in the DDA Regulations of 1968 and the use of the same is not exclusive to the top flat owner. “