If your neighbor sells their property or floors, the new owner is not legally bound by a simple NOC issued by the previous owner.

2)  Draft a formal "Mutual Settlement and Reciprocal NOC Agreement".

3)  The agreement must explicitly state that it is binding not only on the current owners but also on their heirs, executors, administrators, and future purchasers/assignees.

4)  For an agreement affecting immovable property rights to be enforceable against third parties (like new buyers), it should be registered at the Sub-Registrar's office. An unregistered NOC may be considered "futile" for future enforcement.

yes i can do the drafting  of agreement 

Your concern is completely valid. A simple one-line NOC exchanged casually can create complications later — especially if your neighbour sells the property, transfers floors to third parties, or if a future owner refuses to honour the understanding.

A plain NOC is usually personal between two neighbours, does not automatically bind future buyers, can be misused if not properly worded, and does not protect your future construction rights by default. If your neighbour sells the property after obtaining your NOC, the new owner can later deny giving you any reciprocal right unless it is properly recorded in a binding document. Therefore, you should not give a simple NOC letter.

The safest and most legally accepted method in Gurugram and across Haryana is to execute a Mutual Reciprocal NOC-cum-Settlement Agreement instead of merely exchanging NOC letters. This should be prepared on appropriate stamp paper, signed by both property owners, and preferably notarised or registered for stronger legal protection. Such an agreement will grant your neighbour NOC now for stilt plus four floors while securing your equal right to construct the same in the future, and it will bind future purchasers as well.

The agreement must clearly mention that you will have full and equal rights to construct stilt plus four floors whenever you choose without requiring further consent. It should specify that the NOC and reciprocal rights will run with the property and remain binding on successors, purchasers, transferees, and assigns. It should also clarify that by granting NOC now, you are not waiving your own construction rights, and that neither party nor future owners shall object to construction carried out as per law. Additionally, it must include a clause stating that if the neighbour sells the property or any floors, the buyer will be bound by this agreement.

If you give only a simple NOC letter, there is a significant risk. However, if you execute a properly drafted mutual agreement with binding clauses, your rights remain protected even if the property changes hands. Courts generally uphold such reciprocal development agreements.

Registration of the agreement is not legally mandatory but is highly advisable where property values are high, builder floors may be sold, or long-term protection is desired. A registered agreement offers the strongest legal safeguard, while notarisation is usually sufficient but slightly less robust.

In summary, your rights are not automatically protected by issuing a simple NOC. Exchanging plain NOCs is risky. The best solution is a mutual reciprocal NOC agreement that binds future owners and is preferably notarised or registered.

If you require, I can assist in drafting a proper Mutual Reciprocal NOC-cum-Settlement Agreement with all necessary protective clauses in line with Gurugram/Haryana practice.

The NOCs for additional floors often create disputes later, especially when properties change hands.

You can execute a Mutual / Reciprocal Development Consent Agreement. 

Instead of just exchanging NOCs, both parties should sign a registered agreement.

The agreement may contain mutual rights clause. You may mention  that both the properties have equal right to construct Stilt + 4 floors as per municipal rules. You should ensure that your  consent is based on understanding that your right remains intact.

You may include that the consent shall be binding on present owners and their successors, purchasers, tenants, builders, developers etc.  This will prevent the  future buyer from denying your right.

You can engage the services of an advocate either from this forum or outside for the purpose.