Roof access denied

Hello, We recently purchased a flat (UGF) in a builder constructed property which contains 16 flats... 4 flats per floor. Top floor owners have roof rights. They have placed locks on the doors from where other occupants have access to roof and earlier mutual agreement was to ask keeys from top floor owners who wants to go to the roof, for any reason. We all mostly go to the roof to check water in water tanks and few times (1ce OR 2ice in a month) if need to take fresh air with children. Now when we go to ask for keys, everyone is passing us to others stating, that the also have keys why you are approaching us and denying to give keys stating that we are the roof owners and can't keys personal keys to others for general access. As what I got from the other contents that Roof is a common area and available for all, but haven't got any content which states that we others can use the roof generally in case they want to go just to spare time outside their own flat. Also want help, is it permissable to put locks on doors and asking other occupants to take keys from them... It sounds like putting others in a state of mental harrasment and challenging their self respect. Early suggestion path will be highly appreciated. Thanks