Building a single-family house with/without a basement on a small plot

We are currently also building with a basement, but we also have gravel soil and groundwater only at 10 meters! With clay soil and groundwater at 2 meters, I would probably have decided differently, as the risk (even with [weißer Wanne]) of getting a damp basement is certainly given.

The house should be a maximum of 9x9 in size and the garage 10x3? In the drawing it is 9x3, more would not work anyway as boundary construction.

What kind of roof may be built, what are the maximum ridge and eave heights?

What types of heating are possible? Which are preferred?

With loam soil and groundwater at 2 meters, I probably would have decided differently, since the risk (even with a waterproof concrete shell) of getting a damp basement is definitely present.

That is nonsense. As long as the work is done properly, you will not get a damp basement.

Another idea, put most of the technology under the roof (ventilation, heat pump, ...) then you gain significantly more space in the basement/ground floor. For example for a washing machine and dryer.

the house should be max 9x9 in size and the garage 10x3? In the drawing it is 9x3, more probably wouldn't work as a boundary construction anyway. What kind of roof is allowed to be built, what are the max ridge and eave heights? What types of heating are possible? Which are preferred?

We have 3m width on the side. I planned 10m (9m the total depth of the house + 1m to the building line) because I thought it doesn't matter if the garage entrance is directly on the street. Or did I overlook something? The roof is flat, the permissible building height as a maximum is 11m.

There is still a room in the attic, right?

Actually, it's outrageous that something like this is sold as a building plot

Basically, you're right, on the other hand, it's an advantage if the prices are that high (310 €/m2, in a municipality 8 km from the city).