Terrace damaged becoz cracks and sloping issue. our flats facing seepage issues.

A good proposal, which should be acceptable to all affected residents / owners of the property.

Proceed.

Hi Sir, thank you for your response. If they did not consider getting terrace repaired as top priority or because of few flat owners objection. What should be our next step? Please advise

The legal fact is that the unregistered cannot sue nor it can be sued 

If the current office bearers are not responding or not cooperating then you can inform them that since they are not taking care of your current requirement, ask them to return your corpus fund and categorically state that you cannot pay future maintenance amount also.

They cannot curtail the basic amenities, if they do, then you can obtain an injunction order against them through court.

This injunction order can be obtained against the person who is disconnecting the essential services.

Issue notice to the management / association (even if it is unregistered) followed by stop payment of any demand raised by them and file a civil suit seeking permanent injunction and stay order through a local prudent lawyer.

The facts posted suggest the executive committee to be an infomal arrangement. However, the terrace being the commons, the affected persons can join together to sue the others who are remaining passive.

The issue can be solved only if there is a registered body under the applicable laws of the State. If there is no such registered body whom shall you hold responsible to do the work? You send notice to the committee or person who is collecting funds from you for other regular work to do the necessary repairs. If they do not do it you yourself get the repairs done at your own cost. And stop paying the monthly or periodic dues to the unregistered association until you recover whatever that you have spent. Are there other top floor flats who suffer the same or similar problem?

Hi Sir, thank you for responding and sharing your advice. Yes, there are in total 3 flats we are facing same issue similar to me. I am asking this on behalf of all the 3 flat owners.

You can take legal action against the person who is collecting the funds by issuing a legal notice to either repair or to refund the money collected towards repairs, because in the absence of a registered society, one cannot collect corpus funds.