What documents and evidence are required to make a legal will

Dear Sir, My mother was staying in pagdi system house since 1958. It is a private property. In 2009 owner has given the property for re development, since then we are staying on rent.. The problem is 1). the land is neither development nor they have recd any clearance till date 2). owner has not renewed the agreement for last 3 yrs. 3). No rent since Jan 2014. My question to you is my mother is aging and she want to make a will of this property. What documents/evidence are required from us to make a legal will ? Pl confirm.