You need to check the building code (BCA) as a start. There are mandated sizes, heights, natural light & ventilation levels for different types of rooms.
You can register to view the BCA for free on-line here: https://services.abcb.gov.au/NCCOnline/Account/Register
You’ll also need to check your local council regulations & Owner’s Corporation by-laws. You also need to make sure you don’t impact any building fire control systems – e.g. add a wall which stops a fire control sprinkler system working in a particular space.