I will try in a "sweep" without a jungle of quotes to address some contributions / aspects (partly also from the inside of the thread in the green forum).
By the way, the "furnishing" of the site plan with little house symbols, terraces, and driveways does not represent the building envelope, the OP would be freer there. Proposals with nicer floor plans were made to him and would fit into the building envelope, and it should not be due to finances either, but he fears that a nicer house floor plan would lead to a less nice garden floor plan.
Besides the fixation on the house symbol outline – the development plan does not specify an aspect ratio, but the OP mentally clings to this approximate square – there is also a magical size in the room, namely that the employer envisions a home office of about 8 sqm.
Furthermore, there should be a garage. In reality, I consider it more likely that it will be needed as a storage room; but it is supposed to be used for a car, whereas second owners do not appreciate whether it was a garage car. The OP insists that it should be a garage for the car, even if a carport would suffice for the car. But a carport would probably solve a window problem and remove an excuse for the eternity of the search for a solution.
I have already admired the great patience of the BT – as we have clarified in the green forum that this is really a BT and not a general contractor – so much that the OP was annoyed about it.
Personally, I would have told him long ago, "I will now count to three hundred; if you haven’t made a decision by then, you will get a Flair 113 in the flat roof edition."
Ever heard of "further development" or "interpretation/variation of Bauhaus style"?
No, because it is not called that. One could see such further developments with Richard Meier, Ernst Neufert, Mario Botta, Gae Aulenti, Gustav Peichl, or father and son Olgiati. But the example of this BT is not a further development: a kindly put "reduction" from "Bauhaus" to "shoebox" – hardly any misunderstanding is more widespread in architecture than that a flat roof is merely an omitted pitched roof – is not a further development, but a crippling of Bauhaus. Or, as was read here yesterday in another thread: "Bauhaus style."