Building a terrace with wooden decking boards - Which type of wood?

Hello,
we will do the terrace decking on a rooftop terrace ourselves. Since we definitely want to use wood, our question to you is which type of wood is best suited.
The terrace is open above, meaning precipitation falls directly on the wood.
We are also grateful for any tips you can give us, e.g., regarding the substructure and what else must be considered.
Thank you very much for your contributions

Douglas fir or the then more expensive Bankirai wood are fairly weather-resistant, there are also other types of wood. Proper treatment is definitely important, and for the substructure I would possibly rather opt for plastic/WPC. Because especially that part is exposed to moisture. Here, WPC might also be an alternative as a covering, although I personally have to say that you should invest a bit more in WPC if it is also supposed to look good. The cheap WPCs often also look cheap.

Substructure made of plastic or steel, which is sealed all around with Owatrol Cip. Siberian larch wood is also suitable. It is very resistant, slow-grown, and not exactly cheap. Go to a timber merchant for that, not to Bauhaus or the like. They will sell you some fast-grown plantation larch that rots away after five years.

We did it like this:

Drillings with a 125mm earth auger 70cm deep, then short 125mm KG pipes hammered to the same height, about 10cm above ground. Then filled with concrete up to the top edge and smoothed out. These are our foundations.
On top of that, aluminum profiles square tubes screwed upright. On the top edge, recycled rubber in 10mm thickness glued as a spacer layer, cushioning, and dry layer.
On top, self-planed and sanded oak boards with 30mm thickness, because we simply didn’t want monkey wood. Screwed with Spax terrace screws in stainless steel directly into the aluminum tube.

I would do it again immediately, it has now lasted over 10 years without warping or other imperfections.

The protective planting fleece underneath was not absolutely necessary, but prevents plants growing out of the gaps.

Clean setup. Can be replicated.

Take a look at the Sofortholz website, they are not that far from you and deliver without problems. They have a good system for the substructure. We chose Cumaru because of its durability and color. Our wood is currently on the truck and is supposed to be delivered within the next two weeks, then I can say more about whether the system was really such a good decision. The garden landscaper is doing the substructure for us directly, and we will build the terrace ourselves. Douglas fir is also quite okay but not as durable (but cheaper). You just have to decide what you want for yourself.