About roof rights

I, have bought a flat in vasundhara (Newly constructed building). I hv taken top floor with roof rights. All water tank and other usable thing like antenna etc to be placed on separate part of building above staircase n lift area place. So roof is clear for taking my own uses except giving permission to all flats owners to maintain cleanness of water tank etc. My humble submission is as below ;- 1. Builder has given roof rights on Rs. 100/- judicial stamp paper, clearly mentioned that builder has given full possession for roof rights to the buyer of top floor. Is it valid doc sir ? 2. Before selling of flats, builder was assuring to give power of attorney reg. roof rights but now only giving joint DECLARATION in my name stating that we have full possession of said flat roof and can take this for own uses. 3. In future, if required, can I go for temporary or permanent construction on given roof rights area ? 4. After declaration, can builder or other flat owner or govt agency object such construction > Kindly advice. Regards gkumar