The could be quite simple or it might be a little bit complicated. Go back to the original strata plan and if it shows the tub and spa as common property then the body corporate has to retore it.
Even if it’s lot property, there’s a general principle (why may or may not apply in Queensland) that if the owners corporation has to break lot property to fix common property, then it also has to repair the lot property.
You get there’s a little envy at play in this but I think the BC and building manager are wrong. If they don’t want to replace the tub and spa, find a way of fixing the roof without touching them.
It might be different, of course, if the tub and spa were lot property and they were causing the problem. But then again it might not.