Concrete entrance platform - what to consider?

Ok, that may be the case, but it also brings along other significantly more serious problems. In any case, the train has left the station for me. I definitely will not raise the entire area by 40 cm (and install drainage everywhere).

Barrier-free can also mean a ramp ;) (that's how I solved it)

So we also did not make a base beforehand. Since we raised the property anyway, paving was done at the same level up to the door. It was also about access with a wheelchair, which is easier to manage this way. Just before that, a drainage channel was installed. This can possibly catch some incoming "stormwater." The entrance door itself also has an additional seal at the bottom.

Good ramp would work for me then if it ever becomes necessary. But then I would probably rather move. And of course, if one had planned for a single-story from the beginning, then one could have planned it that way. However, the foundation recommendation from the geotechnical engineer was different, and all the experts and neighbors advised against single-story...

This applies especially to wooden frames/posts or solid wood constructions. They "must," according to our house builder / BU, protrude at least 30cm "out of the dirt." Once there is moisture in the base area inside -> very large damage. For stone on stone solid with clinker facade, I often see it at ground level, and I also expect few problems here as long as the base sealing was carried out correctly (probably far too rarely ;))

Yes, standing water or occasional heavy rainfall is not the problem. A drainage channel or even just a slope away from the house is enough. But in Berlin in the last 10 years we had two heavy rain events where you really waded through water ankle to knee deep and subway stations were flooded (I mean once someone even drowned there). Then you're glad to have over 40 cm more before all the rubble runs into your house....

However, the foundation recommendation from the geotechnical expert was different, and all professionals and neighbors advised against a ground-level entrance...

With us too, due to groundwater layers and clay soil it cannot seep away well,
entrance platform with granite edges and paving,
granite stones as a platform at all "doors"