Interpretation of the 1957 development plan <-> possibilities for new construction

I did, though, then traced it as well as possible. The blue line.

Built over is an L-shape (without garage). That is not present in your case.

Thank you very much for the discussion. I am currently in the hotel with extremely poor Wi-Fi. As soon as I can, I will provide larger and additional images from the [GeoPortal].

Good evening everyone,
so, the Wi-Fi works in the lobby.
I have now attached the entire development plan from 1957. There is no more on the geoportal. No legend or similar. And I have not changed anything in it.
Additionally, the site plan, where you can better estimate the position of the buildings also on the neighboring plots.
As I said, I have already measured a little. The house really stands on the building line. Only the garage is not separate as shown in the development plan, but directly attached to the house and set back a bit.
Some of the neighbors have implemented it exactly as in the development plan.
One neighbor two plots south has done something completely different (+1 floor) and apparently got into quite some trouble.

Furthermore, I found a development plan from 1980, which applies to the plots at the southern end of the street.
Therefore, I used the basic assumptions of two full floors, pure residential area, floor area ratio and site coverage ratio, etc....
There would be a legend for this, which I have not uploaded for now.

I am basically interested in the interpretation of the building envelope, without dimension specification.

The statement from the staff at the office was, "If you do it more or less like the new buildings diagonally opposite, then that will be okay."
There are 4 town villas with hipped roofs squeezed onto 2 plots. We do not want that. But it indicates to me that there can be certain freedoms.
(e.g. ridge direction etc.)
The house north of the plot is also relatively old. I assume it will be torn down in the next 10-20 years and two town villas will be built there, too.
But as already commented here on the subject of "belief," "Assumptions are the mother of all fuckups"

Furthermore, I found a B-Pan from 1980, which, however, applies to the properties at the southern end of the street.
Therefore, I based the basic assumptions on two full floors, purely residential area, plot ratio and floor area ratio, etc....
There is a legend for this, which I have not uploaded for now. [...]
The statement from the staff at the office was, "if you do it similarly to the new buildings diagonally opposite, then that will be fine."

Normally, I would say: even the closest neighboring development plan is not decisive and therefore not relevant. Here, however, I think: the municipality does not want to go through the effort of re-planning the area for a handful of replacement buildings in your part of the settlement; on the other hand, if it did, the framework conditions would probably be very similar. Therefore, I consider it "unofficially practical" here to orient oneself to the intent of the neighboring plan – and accordingly, it makes quite a bit of sense to mention its text section here.

Some of the neighbors have implemented it exactly as in the development plan.

I believe you overestimate the significance of the symbolic buildings and their positions in the plan. Only the building boundaries and lines are decisive. From the little house symbols, I would at best deduce the planning intent regarding which plot ratio was roughly considered appropriate as a rule of thumb. Back then, people were not such loophole exploiters as today; they still followed the value framework of the mayor as well as the pastor quite loosely without going too far. So they only built up to the red lines and otherwise positioned a moderately sized house a bit freely. Live and let live, or as the court usher in the 1970s series "Royal Bavarian District Court" put it: "our councilman never sent anyone to the guillotine." In particular, the coupling or non-coupling of house and garage in the plan drawing is not binding.

There are 4 city villas with tent roofs squeezed onto 2 plots. We don't want that. But it suggests to me that there can be certain freedoms. (e.g. ridge direction etc.)

Since city villas have no ridge, they do not violate the development plan. Two houses on one plot do not either, as long as all other rules are followed (floor area ratio and such). I therefore see no freedoms taken that go against the appreciated development plan.

There is no more information on that in the Geoportal.

Yes, that is sad - digital desert Germany

Basically, it is about the interpretation of the building envelope.

The development plan should be repealed because it is geometrically so distorted that it is not even possible to fit it meter-accurately into the current cadastral base. Moreover, the traffic areas were replanned in 1980 by a development plan, so the measurements between the traffic areas and the building lines/boundaries are no longer meaningful. To what extent the authority still adheres to the provisions is questionable. A good planner will find the right words in case of disagreement. However, the approved city villas, which were even mentioned as possible models, give hope that there is no interest in strictly complying with the building envelopes.

There are 4 city villas with a tent roof.

No, they have a hipped roof, whereby the eastern one does not comply with the supposedly specified ridge direction and the two western ones are not within the scope of your development plan, but they also do not seem to comply with the provisions of "their" development plan.

But it suggests to me that there can be certain freedoms.

I see it that way too. The legal situation is at least unclear, so it is not to be expected that the authority staff can make reliable statements (of course, no one would admit that). If there is willingness to talk at the office, the builder, planner, and approver should discuss the possibilities together without putting too much emphasis on the questionable planning law.