It sounds like you are in a townhouse. Is the roof covering other units (in which case it’s almost certainly common property) or is it solely for your home, in which case it may well be your responsibility.
So that’s a question only you and your strata manager or conveyancer/solicitor can answer. Is the roof common property or not? If it is, then the Body Corporate is most likely responsible for repairs unless there’s a by-law that says otherwise.
NB: For those of you who don’t know what roof sarking is, it’s a water-resistant membrane installed under your roof tiles. It acts as a protective barrier, preventing moisture from seeping into your roof cavity and home interior while allowing moisture in the air to escape.