Ownership of exterior portion of apartment building

It is the question of how the building looks like with each apartment owner deciding to paint the exterior of the flat as he/she wishes.  For the simple reason that there should be symmetry and the building exterior should be aesthetically pleasing to the eye, it is better the Society decides a common color for the exterior.

Can i put a banner or hoarding and cctv at my apartment exterior ?

association is not registered and the other owners are saying building exterior is common for all and cannot be used by me.  

They are not allowing to even fix cctv at my apartment exterior buidling.

Society is Registered or unregistered is not the question. It is the question of Apartment inmates living in harmony. For that purpose, certain things need to be decided commonly either through Society or collectively. 

The building is not owned by a single apartment owner it is owned jointly with other owners, outer walls and compound are the property of the co-operative society and the decisions of repairs and colour are taken jointly considering  the aesthetic look of the building. No member individually can take decisions all decisions are taken collectively and in case of differences the rule of majority applies.

Depends on what is written in your property deed.. isn't these conditions mentioned there?? if not, then I think you can challenge it in court to get the things done in your favour.

Since membership of the association is voluntary and it is unregistered, they can just put a social pressure if any thing odd comes in the apartment(s).

Accordingly provisions of State Apartment Owners Act applies to the premises/ owners.

It is better to consult and engage a local prudent lawyer for appreciation of facts/ document, professional advise and necessary proceeding.

For any person, home is his castle. He can deal with it any manner he likes, so long as no (legal) injury is caused to other society members/ other persons.