Hello,
So our property is located in Dortmund. We don't have a contractor agreement yet. We are currently getting quotes. And simultaneously wanted to submit a preliminary building application to speed things up a bit and to have the certainty that we are allowed to build as planned...
Then go to the building authority again and don’t let yourself be dismissed; if you don’t clearly understand an answer, just keep asking until the penny drops. In most municipalities - if I recall correctly, also in Dortmund - Thursday is the designated day for this. And remember, there are only people working at the building authority; meet them with a smile.
I cannot assess the matter of the neighboring dormer and your specifications, as I simply lack too much information for that. It could be that - after building the first semi-detached house - the development plan was changed, or you misunderstood something at the building authority…
Regarding the preliminary building inquiry (BVA), I would save yourself the trouble; although it provides planning security, it only marginally speeds up the later building application. All information regarding the buildability should be stated in the textual specifications for your property. If the official objects, the reference to the exemplary effect of the existing semi-detached house might be helpful – however, it is better presented by an architect than by a layperson. But this presupposes that the development plan has not been changed or supplemented in the meantime.
In my opinion, your options remain to clarify the "gable dormer" situation on your own initiative, to commission your chosen building partner to clarify feasibility, or to commission external building consulting beforehand.
Kind regards