Opinion from experienced people on terrace substrate desired

Good morning,

I am currently renovating my terrace. You can see it in the picture. There were small and thin tiles on the terrace. I have now chiseled off the tiles and the top layer of the wall. Because the new terrace tiles are to be laid up to the edge of the wall. The new wooden posts for the fence and roof will be set from the ground up to the wall.
Over the years, the terrace has settled and has a dip in the middle. Therefore, I have to level between 1cm and approximately 4cm.
The stairs are at the same height as the exit from the terrace door, which will be replaced tomorrow.

My idea is as follows, and I would like the assessment of experienced members.

I would now board around the terrace and mark the final measurement on the wall and the boarding minus the thickness of the terrace slabs and tile adhesive.
Then I would make thin concrete out of gravel, cement, and water and use it to level. And when that has cured, I can glue the terrace slabs on it.

What do you think?

Thank you

Hello xorex

I would be afraid that concrete won't last long.
Use leveling compound. It is made specifically for that. It is not cheap, but it lasts forever. Concrete would certainly crumble.
Otherwise, your approach is effective.

Steven