Rainwater from the roof - drainage in the soil for discharge?

Water should generally infiltrate well.

Have you ever had heavy rain? Otherwise, you would know that what you imagine is nonsense.

Ever experienced heavy rain? Otherwise, you would know that what you imagine is nonsense.

But then it would feel like every second garden is flooded.

The water from the roof must be directed to the house drainage, because the roof area is, on the one hand, significantly larger than the base area, and on the other hand, the area for infiltration is missing where your house stands. That's how I see it. If you are already in the construction phase, this should no longer be an issue, as such matters are usually clarified during the planning phase.

But then it would feel like every second garden is flooded.

In Germany, there is something called a sewage system for that. One to carry away your feces, etc., and another to carry away the rainwater. That’s why the gardens are not underwater. If you don’t have a sewage system, you have to create, for example, an infiltration basin. The basin should be about 10-20% of the roof area (if laid flat). Or correspondingly deeper and therefore not as extensive. It depends on the soil and the groundwater level (which is very high in your case). What does the drainage plan look like that you had prepared as part of the building application? P.S. I already told you how you have to do it:

"Infiltration of rainwater is possible from the bottom edge of the future topsoil (e.g., infiltration shaft or infiltration basin). The base of the infiltration system should be above the maximum water level. It would be conceivable to store the rainwater in a cistern to be able to use it further, and only allow the excess water to infiltrate."

Although "Sickerschaft" probably means "Sickerschacht" (infiltration shaft). You can buy those things. Otherwise: Google infiltration shaft and infiltration basin. Then you will know what it is. Simply letting it run onto the property a) is not allowed and b) will flood your garden and possibly also your neighbors’ gardens. If 20 liters per square meter fall from the sky in an hour, that is a slender 4 cubic meters for a 200 sqm roof, which your garden has to handle on top of the normally absorbed rain. That simply doesn’t work—it then looks like the farmers’ fields. A muddy wasteland!

If you have enough garden area, infiltration (or collecting and using during dry periods) is always better than into the sewer. Normally, municipalities also offer a fee reduction if you infiltrate.

There is no other opinion than that the topic belongs to drainage planning, as already mentioned. How exactly, whether as a cistern, infiltration shaft, or infiltration basin, is almost irrelevant, but it definitely must be planned. And as long as you are still in the construction phase, you should ask the earthworks contractor for an offer. These are things that belong in expert hands.