Building an end terraced house - Which technical requirements should be considered?

All building plots are municipally owned and are allocated in a central application process in March. Therefore, there are no problems in that regard.

Yes, that's how I understood it as well. I meant more that the municipality must also keep in mind during the allocation that BEFORE the signatures are placed on the purchase contracts or the entries in the land registers, the building easement must actually be registered. If the responsible people are asleep at the wheel there, it will be difficult... and it seems that there are always sleeping people at authorities/offices/administrations after all.

That should be possible, right?

Maybe. However, I consider that legally contestable. A building obligation must be project-related and concrete. Furthermore, the purpose of the building obligation is to remedy building law violations of a specifically planned construction project. Here, the building authority is trying to retroactively regulate omissions or even intentional planning liberties of the urban planners, which should actually have been included in the development plan or the design statute contained therein. There is a judgment by the VGH BW from September 2, 2009 (3 S 1773/07), which concerns a different issue, but in paragraphs 53ff the court makes fundamental remarks about building obligations. Depending on the interpretation, as is often the case, other conclusions are possible, but I could imagine the following: The building obligations are registered, the plots sold, and the first building applications arrive. The second builder receives a rejection for his stepped floor with shed roof because the first builder applied for a gable roof and sues against the rejection and the building obligation. The third adapts to the first. The second wins, builds his stepped floor, and the third, who still had to wait for financing or a construction company, suddenly faces unforeseen problems.

I do not understand how such a decision by the building authority can even come about. These are professionals - trained experts. They do only that all day. Has this freedom in the development plan already been successfully tested with other terraced houses? Do they still have a "Plan C" up their sleeve? Or are we all just looking at this way too rigidly? Given the fact that the OP has already failed to find construction partners with his "open to everything" tactic, it is not to be expected that things will go better with other terraced houses.

Without wanting to assess the specific problem here: The people on the administrative side provide legal input. The decision is then made in a committee or municipal council by local politicians, who can have all kinds of legal backgrounds or none at all. However, if this body is willing to "shape" things and gets something into their head, no amount of administrative admonitions that it is not sensible or legally even possible will help.

The mayor could then, in the exercise of his official duty, consider a resolution to be legally flawed and refuse to implement it. The administration could remonstrate. But if in the end the political will still exists, the blame must often be placed more on the politicians than on the administration.

I don’t understand how such a decision by the building authority can even come about.

Shortage of skilled workers. But it doesn’t matter: It’s no different with the lawyers, so that citizens can hardly find an affordable expert who can also enforce their rights in court.

The people on the administrative side are legally correct.

Well, not really with development plans. Politics does recognize that building land needs to be created, but the concept with expert reports, justifications, and legal plans are prepared by the community’s urban planners or, as in this case, an external service provider, where the appropriate experts should then contribute their extensive experience. Politics then only passes the decision. Here, it is not about political decisions but about the professional tussle between planners and approvers, which in this case are even located at different authorities (community and district), making it more difficult. If a citizen then gets caught between the very slowly grinding millstones of two public administrative structures, it can become very unpleasant. Especially since one would probably have intended to use financial reserves—if any exist—more for the outdoor facilities than for months of double burden through rent and financing.

Then the development plan might become a case for the administrative court. : What would apply in the meantime?

The development plan being overturned does happen, but it is rare. Even more so if no objections were raised during the public participation phase of the preparation procedure. Even if a judicial review procedure were pending, the planning law of the development plan applies as long as a court has not declared it void or ordered its repeal. If there is a prospect of success, however, the community would do well to issue a change ban, otherwise compensation claims could arise.
By pressure of lawsuits, I meant lawsuits against refusal decisions or approvals for neighbors that could lead the community on its own or at the urgent recommendation of the approval authority to seek an amendment to the development plan.

I do not understand how such a decision by the building authority can even come about.

I suspect that someone wanted to deviate from the "culture" for a change as a transparency innovation – and then unfortunately as a premiere without practice = experience – to not shove the development of the building area as usual in cronyism to Huber (synonymous with a mayor's buddy) or Häberle (synonymous with a bowling club brother of the head of the building authority).