Timber floor for large Tin shed

G'day guys,

Finally getting to build a decent shed and I want to put in a timber floor instead of concrete (which I currently work on). Shed size is 18m x 12m x 5.5m and is a pre-made colourbond style with portal frames and cladding. The shed company makes a flooring system from gal RHS that runs lenghtways and uses top hat purlins across that. I want to have a double layer of 19mm yellow tongue structafloor as my flooring. The shed is used for boat building and I like to fasten to the floor a lot.

Here's the question.

What is the best way to get a timber floor in that keeps the floor height as low as possible? Am I better off using timber stumps, bearers and joists or going for steel? No issues with white ants here in Tassie.

I have no building experience so would appreciate any opinions.

TIA

AD