Brizylions
firstly what a property is called or sold as has no bearing on the application of strata law. In strata you own the cubic space designated by the insides of walls, and the undersurface of the upper ceiling and the top surface of the lower floor. It could be sold as a shoe bi and the same rules apply.
Generally the roof space and roof is the responsibility of the body corporate, unless a bylaw says otherwise.
However be careful what you wish for. The committee may decide to replace all the sarking of the building, and so may need to raise a special levy which you will have to pay.
As an aside, the sarking provides NO insulation qualities whatsoever. Its purpose is to direct water which may get under the tiles down to the eaves.
Secondly, good luck in pinning the building inspector. In my opinion building reports are only useful to wipe your nether regions. They come with so many caveats , all in small print at the end of the report, that you’ll never win against the inspector.
If anyone is reading this, my recommendation is to engage a builder or engineer and pay the few thousand, as opposed to the few hundred dollars a building inspector charges. You’ll then get a proper report and peace of mind.