One solution to unapproved alterations which end up being asked to be repaired by the Strata is for the strata to check the plans and restore the roof to it’s original size and remove and extension.
The new owner should only be allowed to repair (as opposed to the Strata removing it) the extension IF they get a SBL passed accepting the responsibility for the extension.
If they repair it without an SBL then the work they have done is illegal and they can be asked to remove it at their cost (because they are now the owner who made the change as opposed to inheriting it).