The need for permits is determined by your design.

There are two types of permits:

(1) Planning permit and (2) Building permit

A planning permit are specific to your properties councils required and can vary slightly depending on the requirements. General rules are:

A property with a lot size under 500 sq/m
The property is within a Heritage zone
Building over easement (will also require permit from water authority)
A properties front fence (this is specific to the street and council)
The removal of any significant tree (as deemed by the council)

Generally a Building permit is concern about standard of construction. Works that require a permit are:

The construction of a decking
Any decking structure within 1m of the property boundary fence
An open freestanding pergola within 500mm of any boundary fence
A pergola exceeding 3.6m in height
The construction of any freestanding covered pergolas (gazebo)
The construction of any attached covered pergolas (verandah)
A pergola/verandah located more than 2.5m further forward from the house to which it belongs
A swimming pool or spa with a depth of more than 300mm
A swimming pool safety barrier
Masonary fence exceeding 1.2m within 3m of the street
A non-masonry fence exceeding 1.5m within 3m of the street
A solid boundary fence greater than 2m
A retaining wall exceeding 1m