Yes the roof is common property and it is the responsibility of the Strata to repair it such that it doesn’t leak again. If that means removing the roof and increasing the pitch (or some other method) then it is up to the strata to do so.
At the first occurrence of the problem you might be eligible to claim on the insurance but subsequent flooding is down to the strata and they would be liable for that damage and any further damage to your property.
Don’t blame the SM as they work for the strata and take instruction from the strata.
I’d immediately start proceeding at NCAT against the strata for failing to maintain the common property and ask for all your damage claims to be paid by the strata.
Strata cannot turn a blind eye to design faults and just hope they will go away they need to fix the cause of the problem.
Is the building still covered by the original builders insurance ie less than 10 years old.