Construction of wall, & occupying the common walkway by the co owner of the flat

Arumbakkam, Chennai. My father has bought the second floor flat at 2010. It is actually a 2 Flat building and in that building, the other Flat in the first floor has been bought later by another person. Ground Floor is stilt. We both have registered sale deed & unregistered construction agreement. Builder has equally divided & handed over the UDS via sale deed. Also the builder has allotted 1 car parking to the neighbour and 3 car parkings to me (Only small cars can fit). The entrance to the building i.e the common walkway is situated just next t0 my neighbour's car parking and there is no permanent seperation the builder has made. Now the neighbour is disputing with us and he states the common walkway belongs to him and he also adds he will construct a wall that in that place through which we will not be allowed to enter. When we ask him how to get out of the building since the common walkway is getting blocked he is ordering us to break a wall near to the staircase and asking us to use that. In the motive of acquiring the common passage he is making those statements and also he is parking his 2 wheelers/ cars in that common walkway and making heavy hindrance to come out/ go in to the building. When we go the police station he is telling that since he is having equal amount of UDS he is has the right to acquire the space. Now Kindly clear 1. Is he having any right to construct a wall along with the common entrance/ passage. 2. Is the builder right in allotting more car parking to me more than my neighbour.