Entrance platform with one step made of natural stone

Hello,
I am currently planning to redesign the front garden (I have completely renovated a house and have risen about 10cm). For this, I first want to create an entrance platform made of natural stone ([nero assoluto geflammt]). Since the height from the garden path to the door threshold is 30cm, I need in addition to the platform slab (85x140cm) a step (30cm tread) that runs around the platform.

My plan is as follows:
1) Remove tiles from the existing platform (which is significantly smaller and only 20cm high)
2) Excavate soil for the platform extension 20-30cm deep (the soil has been there since 1980, so I think the soil is firm)
3) Fill in and compact gravel (or do you think I need a frost-proof foundation?)
4) Create formwork for the upper platform part and fill with concrete mortar, let harden
5) Create formwork for the step and fill with concrete mortar, let harden
6) Place natural stone slab (85x140cm) on the upper platform part with frost-proof natural stone adhesive
7) Glue risers frontally and laterally and complete the step as in 6)

I hope this plan provides a good basis for discussion and would appreciate responses. I am uncertain whether the slab can simply be glued onto the concrete analogous to a windowsill.

Hello,

I would just like to raise the question once: Would your project not be better implemented with one (two) block steps made of Nero Assoluto?

I didn't even know something like that existed... But then I would have a joint on the platform above. It looks nicer with a slab.

The slab alone will cost you a fortune... but it's doable. However, we advise against it, as the stone alone for the pedestal and risers cost 2xxx.

1.2 square meters of Nero Assoluto in 3cm thickness with a matte edge cost me 300 euros. But thank you for caring about my budget...

Sorry, didn’t know you live in the quarry. I have different prices from the stonemason in mind here, because our slab 80x120 here with installation and risers would have cost 1,500 euros two years ago. 300 euros/sqm is a common price here in the windowsill format. As soon as it gets particularly deep, it becomes significantly more expensive.