We are going to make our own decking for the roof terrace. Since we definitely want to use wood, our question to you is what type of wood is best. The patio is open to the top, meaning precipitation gets right onto the wood. We also appreciate any advice you can give us, such as the substructure and what else is important to keep in mind.
We did it the following way:
Drilled holes with a 125mm auger to a depth of 70 cm, then hammered short 125 KG pipes to a total height, about 10 cm above the ground. Then poured concrete all the way to the top and troweled. These are our foundations.
Then the aluminum profiles are screwed to this edge. A 10mm thick rubber is glued to the top edge as a distance, damping and drying layer. We planed and sanded the top with 30mm thick oak boards because we didn't want to have monkey wood. Screwed directly into the aluminum tube with screws.
I would do it again in a heartbeat, it has lasted over 10 years without any twisting or other trouble. The protective fleece underneath wasn't absolutely necessary, but it prevents plants from growing out of the crevices.
Douglas fir is quite weather resistant. It is also important to treat the wood properly, and I would choose plastic/DPK for the substructure. This is especially important since it will be exposed to moisture. WPC can also be an alternative as a covering, although I personally have to say that you should spend a little more on WPC if you want it to look good. Cheap WPC often looks cheap.
A plastic or steel construction that is sealed all around. Siberian larch wood is also suitable. It is very stable, slow growing, but not cheap.