It wouldn’t matter where in Australia this was to be used - you would be required to lodge a DA to erect it. That is where the thought police will get you - is it a shed - if so you will need structural drawings. Or is it a garden shed
, which has DA compliance exemptions, but it’s the roof height that will be the Bain of complaints from neighbours in the city anyway that may lead to negative comments on your DA and possible rejection. You can argue that the roof height is only 3.9m at the highest point, and that because it is not uniform and not a constant 2.4m etc it doesn’t fit in the regular slots for DA approval. You also need to convince them it’s not a habitable room LOL, even though you will end up spending most of your time in there