I summarize: the property is free from developers, but apparently it is being sold by a (intertwined with the municipality ?) development agency, and they want to know at the point of sale how one intends to build (?); their uniformity idea originated from the 115 cm knee wall.
Actually, I was roughly satisfied with the floor plan and only wanted tips for or against a construction company
In the end, you will hopefully be glad that you are not being led into this trap here. A construction company will usually not send a co-contractor away empty-handed if they see a chance for an approval stamp - and unfortunately that chance would be given: the building authority would not care about the overtime for your hand-carved interior wall corners; they would give every formally compliant nonsense their checkmark. Decided and announced, the client may be unhappy; and the construction company will put a price on it. Then the bank says the price fits your creditworthiness, and you unlucky one would initially even be pleased. Because neither construction companies nor building authorities employ counselors who would avert such fates. And afterwards, someone stands in their finished botched building and can’t believe that experts did not warn them. But that is not their job. The contractor also has mouths of their family to feed; and the approval officer feels citizen-friendly by not opposing a building wish that challenges their head-shaking if the implementation is approvable. Have we at least been able to shake your satisfaction now (so that you also understand why) ?
If the base data are certain, you communicate them again
As I understand it, the development plan clearly states that the framework is larger; but the seller can still decide on someone else if one exploits the permitted framework instead of the more favorable little witch’s house for him. However, I also consider the latter something that should not be dismissed lightly even with a more clever design. The apparent contradiction at first glance between one-and-a-half and two stories probably lies in the peculiarity of the full story according to Berlin-Brandenburg.