Exclusive use request

I currently have an area outside my lot that is common property but can only accessed by maintenance people for access to the roof and to abseiling hooks. No other residents could ever access the area. It is on the top floor with two other units, not close to this area.

That space is approx 50sqm that is covered by white pebbles and underneath a solid concrete slab – with drainage.

There are 3 air con units that constitute approx 10 sqm with plenty of space around them with a thin metal shield on the eastern side.
to the south they extend out from my baclcony by approx 2m.

To the right of these is an access door from the internal boiler room and access to the rooftop via ladder.

Further to the east is a large space that is approx 15-20 sq m that is empty and contains a corridor to a downpipe on far eastern side.

To the north of this I have my 4m x 4m balcony (on title) that I would like to extend by 2m x 4m (to the end of air con units).
This would entail me paying for the dividing fence to be relocated and extended to the east and pushing existing pebbles back to common area. And making pretty the space where the air con units are.

At this stage I cannot see any reason why it wouldn’t be granted (however I don’t trust our Building Manager to make something up).
There are still 1.5-2m corridors of access.

How would I go about requesting exclusive access to the extra 8 sqm and to allow the fence movement?

Thanks