I am in NSW.
As Sir Humphrey said, the strata plan ( available from LPI) determines what is common property and what is lot property. Thick lines generally show common property boundaries and thin lines are just dividers.
Be aware that the date of when your strata was registered (pre 1974 and pre 1986) have an affect on interpretation of common property.
Also read the bylaws as there may be exclusive use bylaws affecting common property.
To amplify what Sir Humphrey said,, the committee under no circumstances determines what is common property and what is not. They can choose to,interpret the strata plan, but you can challenge their interpretation.
That may require a good strata lawyer to help you and a visit to the tribunal.
BTW the strata plan is attached to your contract of sale if you don’t want to pay at LPI