New single-family house in southern Germany

If the building height is roughly the ridge height, a gable roof with a 30-45 degree pitch is only possible without a knee wall and the rooms upstairs are hardly usable. Therefore the designation as a glorified (=better) attic.

a gable roof with 30-45 degrees is only possible without a knee wall and the rooms upstairs are barely usable.

I see that as an exaggerated conclusion. Knee walls are less enjoyable in buildings following the energy saving ordinance, but fundamentally there are worse disasters than a low wall instead of a knee wall. In a non-full floor, you don’t have standing height across the entire roof cross-section anyway. 30° without a knee wall only suffice for a small attic studio, but 45° was regularly inhabited without a knee wall in the past (and they result in a one-and-a-half story house that deserves the name computationally).

Maybe it's a bit exaggeratedly phrased, but I think there are reasons why nowadays people don't pull the roof all the way down. They have also done away with the great crawl spaces at the knee wall. And the calculation above was for 30 degrees to get as much knee wall as possible. At 45 degrees, the roof would have to start even lower or the house would have to be narrower. That's why I still assume that it rather means the eaves. I haven't received an answer yet; if nothing comes by tomorrow noon, I'll have to call.

Isn't the text version of the development plan available online? In times of Corona, it should be mandatory. Your plan section is also not exactly legible.

but I think there are already reasons why nowadays the roof is no longer pulled all the way down. The great crawl spaces at the knee wall have also been abolished.

"Crawl spaces" sounds much more charming than "Abseiten" :) The architectural-cultural reason for the switch to knee walls was – long before the builders became "standing-height addicted" – simply that both knee walls and dwarf walls are just byproducts of the respective roof structure construction variants. Jamb walls have disappeared about sixty years ago. The reason why nowadays one completely turns away from the previously only fadingly popular dwarf wall lies in the Energy Saving Ordinance: the dwarf wall variant offers less roof room width for the living space but provides the storage space of the Abseiten. Maintaining this culture would be an unpleasant fiddling with regard to the "thermal envelope," which one gladly omits – and without the use of the Abseiten, the dwarf wall is on balance just annoying. Furthermore, with dwarf walls one can only do dormers with the classic over-the-beltline knee wall parapets, but today one prefers to be able to make cross gables with floor-length windows. Which I can understand – even a small dog wants to be able to look outside sometimes ;-)

I haven’t received an answer yet, if nothing comes by tomorrow noon, I’ll have to call.

I wish you clarity soon, because what is really meant there does make a difference beyond just the comma (however, administratively "the written word applies") ;-)

It has been a few days since I last wrote something here. In the meantime, quite a bit has happened.
Regarding the building height, I called. The responsible caseworker also thought that the eaves height was probably meant. That means free rein for the large attic, as the basement is basically out. As much as I would like to have it, it is the cost block that makes the big difference between sleeping peacefully and a tight budget. I do assume that I could also increase the budget from the bank, but actually, I do not want to. A pantry can still be quite well accommodated in a storage room under the stairs, and for the technical room on the ground floor, we have now also found some floor plans. If in doubt, the study room will have to shrink a bit first. According to the current status, probably only a massive ground replacement could bring the basement back.
As for the ground... that is currently my biggest problem. Since the plot is only reserved but cannot yet be purchased, I cannot just commission a soil report to get clarity. On the other hand, I find it problematic to commit to a planning now that presupposes the ground is good. I wanted to call the municipality in the next few days to see if anything is known and possibly ask one of the future neighbors the next time we are on site again. Unfortunately, with the great weather, there is rarely anyone outside... Any other ideas on what can be done to narrow this down? Given the current status of the development, I also took a photo of a larger ditch; if that helps, I can upload it.
Regarding construction partners, I have picked out and contacted two local general contractors. One has not responded at all so far; the other is already fully booked for next year. That perhaps speaks for the contractor but does me little good for now. I have now found and contacted a third one; let's see what comes of it.
Otherwise, the first offer from Schwörerhaus has arrived. At first glance, it seems okay and within budget, but upon closer inspection and in direct comparison with the Weberhaus construction service description, it becomes apparent that some corners are cut in some places. Nevertheless, we will continue to pursue it for now; however, we definitely need to talk again about floor plans apart from promotional houses.
The conversation with Weberhaus on Friday was pretty good; first talked for a long time about wishes and then about the floor plan itself. The whole thing is quite expensive but also has a decent standard where I feel that the upgrades are more cosmetic than functional.
By the way, I have now reached a small booklet in which all my thoughts on the topic of house building are more or less organized and recorded. One topic, one page, and as soon as something occurs to me, I try to enter it. It is definitely clearer than the previous paper chaos. At least so far.