Common terrace maintenance

Hi, I live in a stand-alone apartment in Kolkata, at the topmost floor. Due to 2×1000L water tanks residing immediately above my roof, my floor has suffered heavy damage, and cracks, because of which rain water seepage has damaged various portions of my flat. The builder has refused to take care of this issue, and it has fallen on us to bear the total cost of roof repair and treatment. The amount is approximately INR 2L. This involves shifting of the tanks to the staircase roof, and being replaced with 2x500L capacity water tanks, along with necessary plumbing work, masonry work and chemical treatment of the roof. None of the other 3 flat owners residing in the building have contributed a single penny towards this cost, even though the maintenance is for a common space of the building. Now they have the audacity to put blame on us saying we have incurred this cost unnecessarily, and are refusing to pay the money. Please be informed that before starting of the work, we had cited the advise of KMC certified ESE, and he had also given us the go-ahead to proceed with this work. We had even informed the other owners regarding this work an innumerable number of times over the course of 2 years but had received no response from them. Instead they always used to find some or the other excuse to avoid helping us in this regard. My question is: 1) Is it legal to refuse paying for this common area maintenance cost? 2) Can I limit access to the other owners of the building to the common terrace, seeing that I alone have paid for its maintenance? Please be informed that even after this we have allowed people for maintenance to the common terrace. My second question pertains only to the owners of the 3 below floors, and their immediate family, friends and relatives. Any answer would be appreciated.