Property dispute - partitioning a leased joint property among brothers

Dear Madam / Sir, Myself and my borther have a immovable property at Salt Lake, Sector-I Kolkata700064. Originally it was a 999 years’ lease property acquired by our parents from the Governor of West Bengal. Consequent to the death of both the parents, the property devolved to us. Thereafter, by mutation, myself & my brother became joint holders of the same. Presently it has a ground floor bungalow of 1375 sft area (can be extended to about 1600 sft including the present structure). It has a bed room in the first floor and an unfinished washroom area. Other than these, it is basically a single floor (ground floor) bungalow. As per old sanctioned plan, we have provision to add two more floors (1600 sft area of each floor). It was mutually agreed, after lot of deliberations, that my brother would take the existing ground floor and extend it as per permissibility. And I shall build up the entire first floor. Accordingly, we approached a lawyer to initiate a case so that we can partition