Construction financing for house sale

I read inheritance there and I believe no speculation tax should be applied. Because the purchase date of the deceased applies for that!

First of all, thank you very much for your answers, they have already helped me a lot. Now the situation is not quite simple. My brother definitely wants to build on the neighboring plot (also approx. 400 sqm). If he decides on a semi-detached house, that would decrease the value of my plot, since the buyer can no longer freely decide how their house should look. Is that the case? If so, this leads me to another question: The plot is about 11*36 (a little more). Would it be – according to your rough estimate – possible to build a single-family house on such a plot? Minimum distance is 3m, 2 full floors, floor area ratio 0.5. Thank you very much for your competent assessments.

Speculation tax only applies if under 10 years. However, this period does not start with the inheritance but with the deceased. Is there a development plan? Simply placing a semi-detached house on the boundary is not possible. The plot seems quite narrow. A single-family house would also be very narrow and elongated. If the future owner wants and the development plan allows it, a semi-detached house could still be built. I think the sale should be completed before your brother submits the building application....

At a width of 11m, it can be assumed that no detached single-family house will be built there.

Yes, there is a development plan. However, the two plots are still drawn as one and the ridge direction is parallel to the current long side (I hope I was able to express myself clearly). Apparently, numerous exemptions from the development plan have already been approved, since it dates from 1983 and is therefore no longer entirely up to date. At least that is the statement from the building authority. I already thought that 11 to 12 width would be tight.

Sell the entire plot to the developer who will build the semi-detached house. Your brother can agree on a right of first refusal on one half.