3-story house required.

I could basically build like the White House and put in 2 large dormers if I am allowed to build them. And then the house is considered 3 stories?

No, this neighboring house is two stories, both on the plan (a boundary between two development plan areas runs between the properties) and in reality. However, his property and the one next to it toward Behringstraße belong to the area of the "first amendment" – whether built before or after, I don't know, but the shape of this amendment would be interesting. The aforementioned houses on Eintrachtstraße are probably three stories (of which I cannot see if they still belong to the same development plan). But as I said, I suspect they obtained an exception for the dormers and then fulfilled the full story requirement with the dormers.

However, his property and the one next to it towards Behringstraße belong to the area of the "first amendment"

Doesn't only the black dashed area belong to the 1st amendment?

Because the roof pitch is probably also prescribed

Yes, sure, but the neighbors also did not adhere to that.

The house in the first picture has a mansard roof

No.

It is not a multi-family house area

Area might be overstating it, but for your plot the city planners have clearly designated a multi-family house. Therefore, it could be difficult to obtain the same exemptions as the neighbors, who, although they have dormers and obviously exceed the roof pitch, at least have built multi-family houses. Your single-family house will not please the city planners.

You should consult a planner or architect about it.

Or the urban planning office, since they ultimately have to grant exemptions. Find out here why the neighbors were allowed deviations in roof pitch and roof structures and what the prospects are for your project. Without a formal building inquiry, this is not legally binding, but it should suffice for an assessment of the potential for conflict.

Doesn’t only the black dashed line belong to the 1st amendment?

Yes. Since a sale is out of the question for you and you have not given any reasons for your statement "Because 3 floors basically do not come into question," an architect can certainly design a single-family house fully compliant with the development plan on the plot. Of course, that is far from standard.

Doesn't only the black dashed line belong to the 1st amendment?

Pardon, yes, that's right: the white house is number 7, which is already outside the amendment.