The Owners Corporation has the right to gain access to your lot in order to inspect and repair or service common property.
However, you can demand that they get orders from NCAT requiring you to give them access every time they need to do so.
I’m not suggesting you be deliberately obstructive but this is a situation that might require some leverage – and that’s yours.
So, taking a more positive position, put a motion to your committee that they create a new access point on common property.
If they refuse, or show signs of dragging their heels, tell them that you will make it as difficult as possible for them to access the roof through your unit, every time they need to do so.
In other words, it’s going to cost them something whichever way they decide to go, and they wouldn’t want to need your approval in an emergency, so they may as well fix the problem once and for all and move the hatch.