I am cheating a bit on this post because truth is I am already quite far down in the construction. Mind you it has taken me a while to get to this point. So far the main deck is complete with one of the staircases, with the two bigger still ones to go.
The main deck is 4 m wide and about 15 m long with 3 sets of stairs (one wrap around). We opted for 90mm Garapa decking which we chose to lay smooth side up and to leave untreated. Fortunately the wood seems to be properly kiln dried so has showed little signs of splitting.
With regards to securing the deck I found nifty fixing system which is almost hidden and doesn’t require any screws through the deck. The resultant look is a very smooth clean finish.
It terms of support I used 2 rows of 75mm pole droppers + the wall of the house where possible. The poles support two main beams (225x50mm), with 150x38mm beams running the 4 m width of the deck at about 450mm centers. The result is a very stiff and stable surface surface which is great – I hate it when there is give on a deck because the design has skimped on support beams.
The most difficult part was definitely getting the planks to run in straight lines as this would be very noticeable on a 15m run. The whole operation was made easier by using the plank lever which lets you squeeze the planks together, however the method that I eventually settled on was to lay 5 or 6 rows of planks with the clips installed but not screwed down. I would then run a gut line about 50mm ahead of the last row with same offset from the house. Using the gut line as a reference I was able to make a mark on each bearer representing a straight run. I then made a wood spacer equal to the smallest of the measurements made from the gut line mark to the last row of decking. Then working form one end with the plank lever and the spacer as a reference I then fixed all 5 rows to the bearer. This way any deviations are corrected over 5 rows as the clips tended to space the planks evenly. I have included some pics below showing progress so far: