No he will not do anything

RWA has right to decide the affairs of building and object the change in actual plan/usage of building. It is fine that you are top floor owner, no hindrance to other owners but than they will also make change following you and this will create mess.

So installation with RWA permission will be good.

Well, you are top floor owner, some benefits attach you whcih are not available to lower floor owners, so you have right to install at outdoor.

Law says that your object should not be in the the way of anyone.

You can install if it doesn't obstruct anyone's way

You can install ac outdoor unit outside your flat

builder should  not have any objections regarding the same 

however you cannot install it in terrace of the building 

No worries.  No issues. 

The question arises where and which part of building do you want to install out door unit of AC ?

Whether the installation is full proof of safety measures and non-accidental conditions are checked with experts?

There is no law on this point. You may request the RWA to permit you to install the outdoor unit on rooftop without any hindrance to anyone.

1. Any deviation from the sanctioned building plans shall invite prosecution from the Municipal & Fire Dept. authorities.

2. You are advised to obtain permission from Municipal & Fire Dept. authorities, for your purposes, which shall be Final & Irrefutable and the RWA cannot object thereafter.

Any alteration to the structure or such installation, you may have to obtain the NOC from the neighbors as well as RWA.

You can convince them about the issue and can inform them that you assure them of compensation if there is any hindrance to anyone due to this.

They can't legally do that

You can install AC Outdoor outside your flat. 

No residents or RWA cannot object to you for installation of your outdoor unit at terrace because it will cause no obstruction to anyone in the building.

Dear Sir/Madam,

You are suggested that RWA or residents are not supposed to stop or create issues in installation of the AC. You may complain regarding this to registrar of society. 

- If the said installation will not create trouble for the neighbours and not in the common area , then you are free to install the same as per your requirement. 

Yes if it cause any nuisance or harm then they can object.

They cannot object without any valid reasons. They have to show that it is a danger to the stability of the property or something which is dangerous.