Illegal posession of my property.

My father sold a property to a person, a shop in ground floor and complete second and third floor. I was in Pune completing my graduation. After returning, I got busy in my own work and dad used to take care of our properties. After my dad passed away in 2007, I never realy looked for the property papers. Around 2012, I got the time to look into the papers, the copies of some sale deed was missing including this one. I asked for the copy to this person several times, but he never realy had any intent to provide me the same. He said that my father sold him to sky high, and due to long family relationship I trusted him. Then an year ago,he started construction of the fourth floor and I helped him in all aspects. Later I applied for a certified cop, after going thru it, I found that he had illegaly possesed the fourth floor, my dad sold upto third floor, and fourth and above belongs to us.I talked to him and asked him to return and said that the construction cost incurred in fourth floor will be paid to him by me. I tried to settle the issue but all in vain. What shoud I do? Can police register an FIR in this regard? or file a case in a court?