I built a deck over concrete alfresco at last house because I thought would be cheaper than tiles.
I was wrong by the time I bought frame brackets screws and hardwood decking boards it came to about $200 per m2.
Decking boards alone are $4.95 per meter so say alfresco is 20m2 and 5m X 4m. We go 5m lengths and then each board is 90mm wide. That's 4000 / 90 = 44 boards that are 5m long that's 222m of decking. At $5 a meter that's $1,100 for decking boards.
Frame for that size would be $800ish for T3 pine.
Up to $1,900
Fixings and brackets add another $100
$2,000 now.
Stain $200
$2,200
That's probably conservative. It would also take a DIY person approx 40hrs to build it.
Your over $100 per m2 already that's doing yourself.
Then you need to spend potentially $200 a year to restain.
In 5-10 you may need to replace boards or frame if a lot of water gets into them
Furniture doesn't slide on deck well and also need to do a 50mm barrier away from house bricks for termites.
Other hand can get tiles for $20 per m2 than laying $40 m2
So that's $400 tiles and $800 laying
If your handy you could even lay yourself.
And they practically last for ever.
I'm tiling mine myself and my father in law has tiles they are easy to clean creat an inside out feel