What to do if their is dispute of property

my father gave 2 guntha land for development to a local builder for illegal construction of 4 floor. as per oral understanding between builder and my father, builders gives possession of 7 rooms to my father but there is no ownership document between builder and my father for that 7 rooms and no property tax so my question is that what kind of document will show the ownership of that 7 rooms in favour of my father ?