There aren’t many, if any, laws around parking spaces – they tend to be covered by by-laws which vary from building to building – but there are laws about common property.
The simplest solution would be to commence action against the strata committee for failure to enforce its obligations to maintain and protect common property. This would probably be under Section 232 (2) of the Act.
But initially, you and other owners would have to request mediation at Fair Trading and the prospect of having to defend his little land grab might be enough to see the cage removed.
By the way, there’s a reason we have fire regulation in our buildings – it’s to stop people dying in fires or getting hurt while fleeing from them. Concern that they might have to upgrade their fire safety measures should ring alarm bells in itself.