You really need to check with your local government.
Just go to your local council website and search 'building permit'
For example, our locate government (City of Greater Geelong) does not require a building permit.
Here's what they say:
Construction of a freestanding Class 10a building (a shed, carport or garage) is exempt from the requirement to obtain a building permit by item 1 of Schedule 3 providing it:
- has a floor area not exceeding 10m2; and
- is not more than 3m in height, or no more than 2.4m in height, or within 1m of the boundary