1. Well, if the building pan is duly sanctioned then it is considered to be safe. However do take information whether conversion of such land is prohibited or not.if no such prohibition is in place then conversion is a matter of time.
2. If the owner has valid title over land and all the necessary permissions and licences from the concerned public authority then it should be safe to proceed with.However while proceeding further do make a proper agreement with the owner.
3.No purchase of any proeprty is advisable without getting all the documents checked from a local lawyer.
All the best.