Planned new single-family house - floor plan available

"elongated cuboid loses more heat than compact cuboid"

Then it is best to build a spherical house, which has the optimal ratio of volume to surface area. If you insist on right angles, you do indeed end up with the cube.

This house is an extreme matter of taste, and taste is known to be subjective. Honestly, it would not be my choice at all. This rugged shape, the flat roof and the captain’s bridge on top... but the OP has to like it. The criticisms, small children’s rooms and mini bathroom downstairs, parents’ area very unfavorably zoned, have already been mentioned.

I suspect that if there is a budget overrun, we are not talking about "small change" here; the cost drivers have already been listed. I find it hard to imagine building this complicated form, including the green flat roof, even remotely for €450k. Even a €15k “buffer” that accumulates is practically nothing. In addition, it was mentioned in passing that they want to manage the whole project with €3.2k net income. The project then requires a very high commitment of equity capital.

they want to manage the whole thing with €3,200 net.

Is that so?

They should have healthy legs...

If this keeps going like this, my next topic will be "looking for an architect"

Yes. Now...

As already wrote, the site plan is nice and good, but it's worthless without a legend. What I can make out, however, are contour lines. And not just a few? You wrote there is no slope. With a 5 m difference across the property, I would rather speak of a (down)slope. If that applies, the design wouldn't be feasible anyway.

Then the best thing to do is to build a spherical house, which has the optimal ratio of volume to surface area. If you insist on right angles, then you indeed end up with a cube.

I would not consider this extreme desirable in reality – but also not exactly the opposite, as planned here. If you then want not only to heal that but even convert it to KfW40+, the builder might as well order his next Porsche twice.

What I can recognize, however, are contour lines. And not few? You said there was no slope. With 5 m across the plot, I would rather speak of a (down)slope.

Between two solid contour lines there are four dashed ones – so probably 20 cm each, and the five together stand for one meter. But it remains an image that only those who know what it’s supposed to mean can "read."

I wouldn't consider this extreme desirable in reality – but also not exactly the opposite, as planned here. If you not only want to cure that but even convert it to KfW40+, the builder can order his next Porsche twice over.

Between two solid contour lines there are four dashed ones – probably 20 cm each, and the five together represent a meter. But it remains a little picture that only someone who knows what it’s supposed to mean can "read".

Ok. I just thought the 56 and 52 were meter readings above sea level. For Lower Saxony, that is possible?

Currently, I save at least mind. 1.3k every month. The buffer is thus further increased, even if only slightly. With a net income of 3.2 and fixed costs including rent, electricity, insurance, etc. of about 1.1, this is very feasible.

For