community of owners

Hiya, buying flat on brand new development with terrace above that will be owned by community of owners. My contract says i have exclusive use of terrace but once we move in and the community of owners is set up, how do i know that my contract will not be overruled and everyone will be able to use the terrace?
i was told before i paid my 10% deposit that the terrace was mine but it seems now that i will not be the owner? Obviously no community statutes are set up yet until we all move in in october but how does this affect me legally? Any help would be greatly appreciated.....