Expansion of the attic in a hip roof as a basement replacement

Thank you very much for your input, but I would probably need some clarification on that. [...], why a complete misplanning?

We found the visualizations very appealing

No, "complete" faulty planning may be the case, but thanks to the withheld "remaining 90%" ;-) of the presentation, it cannot be fully appreciated in all its glory. Planning a built-out hipped roof (levels two and one of the unaffordability rocket) on a T-shaped floor plan (level three), equipping it with a knee wall (level four), and still talking about cost motives points to a faulty planning in the sense of a fully exploited naivety privilege of construction laymen. "Schilling - not Dollar," Falco once sang; here it’s reversed. I am unsure whether I should read Katja’s proposal to also crop the hipped roof as fine irony.

... which makes it all the more incomprehensible not to let us enjoy it. We certainly do not dislike Sim houses, we just do not debate them as if they were supposedly buildable proposals.
That the "dream house" from the perspective of a Sim house visualization programmer is an (ultimate) delicacy, I gladly believe - but unfortunately that does not make it more buildable (nor affordable either). The castle-in-the-air bonus in construction financing only exists on April 1st.

but in this matter, objectivity simply helps me more. Otherwise, I could also ask in the part-time cabaret forum what they think of the idea. [...] And yes, it was probably naive to assume a cost saving with the DG variant. Here is a visualization from the outside, feel free to share your professional assessment:

… The roof casts a lot of shadow. In my opinion, there is too much eaves.