Common Terrace Usage Right

No, no legal right to do so.

No, it is illegal. Register a Complaint Against Housing Society/Any other Trust/ Professionals as defined below. ================================================================== https://www.icrpc.org/icrpc.org.contact.htm

if they are also have the right to use the terrace then it can create problem other wise no matter

One can't be permanently banned but could have ocassional restrictive access to the barsati floor to check their water tanks,pipelines, etc. This comes under easementary right. Although, its not a common area for other flat owners.

Dear Vinayak, In the facts of your case you need to check whether the apartment owner have exclusive and sole right over the terrace, if not, he cannot stop access to others. Request you to provide me further information for an effective remedy.