For a 2.4 x 1.8 x 2.1 shed, expect to pay around the $450 mark, extra for delivery and installation..
A flat or skillion roof may be slightly cheaper.
You could go timber but that will set you back 3 times the cost ot zincalume or colourbond.
A couple of suppliers in Sydney:
Col Western:
http://www.colwesternsheds.com.au
Stratco:
http://www.stratco.com.au