Hi @GEOFFBALL,
A warm welcome to the Bunnings Workshop community and thank you for your question.
There are metal decking systems such as Steel-Deck or this Quick Built 3.6 x 1.2m Modular Steel Deck that can be used with timber decking.
The only real difference is the fixings you would use to attach the decking boards. Instead of a timber decking screw, you would use a metal decking screw like these Simpson Strong-Tie 4.8 x 50mm 10g Metal Decking Screws.
Let me know what you think and if you have further questions please don't hesitate to ask.
Jacob
