Finished floor, how high above street level?

3 steps out of the dirt is stated in the construction regulations from the imperial era. I would not recommend anything else in times of climate warming.

So we are with the finished floor 10cm above the level of the sidewalk which starts only 3m away. Normally, it is said that any building openings that are not watertight against pressure water should be above the backwater level. In our case, for example, the backwater level is published on the city side in planning notes and is actually at the height of the sidewalk, since we have the Danube and flood hazard areas in close proximity. In 1999, the water of the Danube practically reached the front door. But since we want to enter the house "barrier-free" (the front door is 6m away from the sidewalk), we will have a slight slope from the front door to the sidewalk so that we can enter the house without stairs.

For such topics, I would look at long-term data on groundwater levels, high water marks of nearby streams and rivers, as well as extreme precipitation. If data emerge indicating that there is a frequently increased risk, I would basically plan the finished floor a few centimeters higher. Then design the basement accordingly watertight against pressure water if one is desired.

Since we occasionally have to deal with surface water during very heavy rainfall in a short time (the sewer of our side street is underdimensioned), we have a drainage channel along the entire west and south side of the facade that drains into a high-capacity soakaway shaft, which is independent of the street sewer. This way, during heavy rain events, we do not risk water running from the street into the house through the windows after it has overcome the 10cm height difference.

Personally, I would not place a house within such "hazard zones" lower than the street or sidewalk level.

The development plan tells you, in case of doubt the building authority, how far above street level you are allowed to place the top edge of your finished floor... and often also how far above you have to place it(!). I have to build at least 15cm and am allowed to build a maximum of 60cm above street level.

And even if some here probably see it quite differently: Build as high as it is economically/financially sensible and legally permissible. At some point, the question arose for me that if I build even higher, I have to support my property towards the neighbor. Then the money ran out eventually, otherwise my finished floor level would now be 60cm above street level, instead of a good 20. This is one of the few things you can never change again on a house. And it certainly doesn't hurt during the next heavy rain if you lie 30cm above the street instead of 15cm below... and then ideally a fully sealed paved surface in front of the house, with a small drainage channel at the lowest point ;)

You also always have to keep in mind that you will later fill in terrain and that this ideally should not extend beyond the foundation slab... otherwise the vapor barrier under the first course of masonry won't help much if you throw damp soil right against it...