It's best practice to have as much gap under your timber as possible @Faheem. That's why I was suggesting the single-level structure with the pedestal feet. It gives the maximum gap under the timber.
Thank you @MitchellMc (once again)
I will go with the single level deck then with pedestal footings. So If I understand this correctly, I can have pedestal footings at 1 meter distance from each other. This mean at the area of 4.6m*5.2m, do I need roughly 50-60 pedestal footings?
And my another question is if I want to create a picture frame style around the merbau decking (refer above photo), I understand i need extra joists. How far those joists on the edging should be if i use 140mm merbau for the borders and 90mm for rest of the area.
It will be best if you sit down and draw yourself up a plan to work off @Faheem.
By my brief calculations, that sounds about right. By taking your 5200mm width and dividing it by 450mm, you get 11.5 or 12 joists spaced across the area. Each joist will have approx five pedestal feet over the 4600mm length.
For the double joist, I'd recommend spacing the two 45mm thick joists 100mm apart. You'd use short, cut up pieces of your joist, positioned every 450mm where the picture frame piece needs to be nailed off. I'll include a rendering I created for you below to illustrate. Please note this is a 3m x 3m deck drawn to scale.
Thank you so much @MitchellMc. I think I have got answers of all my questions. Much appreciated. And thanks for the drawings 😊👍🏼