Don t buy adivasi land, adivasi land can be traded only amongst adivasis. Any transactions outside of that are not legally valid, unless taken over by the Government for projects or as part of a land acquisition scheme. There is no concept of a 99 year lease or so. You will have no title rights what so ever if y buyb a adivasi land. Someone might be taking you for a ride. Best consult a good property lawyer, I am sure he will provide you the same advice. Please keep me posted.