Capital gain on tenancy propertt

tenancy flat was converted into ownership of property by lanldlord of building than after five years building went for redevelopment and new flat was given with additional area. what should be cost of property. M.V. can be considered when landloord converted into ownnership property??? no cost has been paid to landlord. now if property is sold (by tenant) what will be cost price of flat to be considered for capital gain