I have come across many cases like this. Look for your property documents. You will get a answer of many of your questions. Still you can sue the builder for the damages done to your flat.
Please understand that terrace is a common property and builder cannot restrict others to access to the terrace.
To take legal action you have many options.
You can complain to Real Estate Regulatory Authority(RERA) in Karnataka. RERA help those people who suffer from the malpractices of builder and to safeguard the interest of people.
You can visit the following address in Karnataka to make a complainant against the builder-
1/14 3 cross mission road silver jublee block csi compound unity building, Bengaluru, Karnataka
You can also send a legal notice to the builder to comply with the norms. All legal action can only be taken once notice has been served upon the entity or individual you wish to take to court. It is only this process that legalises bringing a matter to court. The intimation sent is known as a legal notice.
A legal notice is, therefore, a formal communication to a person or an entity, informing the other party of your intention to undertake legal proceedings against them.
This notice, when sent, conveys your intention prior to the legal proceedings and thus, makes the party aware of your grievance. Many a times, a legal notice served will bring the other party on heels, and the problem can get resolved out of court too, with fruitful discussions on both sides.
And, if the other party is still not heeding to the grievance, one can always start the court proceedings after a particular interval, as stated by the law.
Although a legal notice can service as a purpose of negotiations between the parties and save time, effort and money that are usually spent in court cases.
SHRI GOPAL VERMA
ADVOCATE ON RECORD
SUPREME COURT OF INDIA