Development plan full floors / floor knee wall?

Our question is rather, are knee walls up to 50 cm allowed, or can they also be higher? :)

No. Top of ceiling/rafter bottom edge... results in an interior knee wall of roughly 65 cm, however I don’t know if by top of ceiling they mean the raw floor or the finished floor.

If you put interior walls on the upper floor, that can raise the knee wall. Of course at the expense of living space. But you won’t be allowed to exceed the exterior dimensions of the knee wall. Have a look at 'mansard roof'

You mean a dwarf wall. Knee wall knee wall outside, dwarf wall inside :)

I have meanwhile read the development plan in both parts and must withdraw my initial assessment, as the TE had cited it misleadingly (because incompletely). Unfortunately, it is clearly meant here that a gable roof with a pitch of 42 to 50° is to be placed on a single straight-walled storey, with a knee wall of 50 cm practically allowed (i.e., without quoting the entire litany here in detail and calculating this and that back and forth) to be effectively inside (from the finished floor level) also about 50 (or perhaps at most sixty-three) centimeters, and the second full storey here is only meant to indicate that a certain reduction in floor area compared to the ground floor does not also have to be observed. As a result, I see here on the raw ceiling two rows of bricks under the foot purlin, and inside a Franconian vacuum knee wall. I would also make this knee wall and recommend not adding a dwarf wall after it, but only carrying out a boxed-in area behind the WC / shower or similar. A (dormer) is permitted but would already be needed for a staircase rising on the eaves side. Therefore, most of the rooms in the attic will be dependent on roof windows on the eaves side.

from finished floor

Thank you, that answered the last question.