1. All the flat owners have the right to use the roof whereas the owner of the land might have the right to construct additional floors thereupon subject to getting sanction from the local Municipal Corporation.
2. Actually you should have examined the Mother Deed before buying the flat.
3. However, there is hardly any chance that the Municipal Corporation/Authority will sanction any plan for constructing additional floors on your roof for which you need not worry much now but should keep an watch on the further steps to be taken by the land owner and the developer.
4. Please note that even if additional floor are constructed, all the flat owners shall have right to use the roof of the top most floor.