Neighbor wants to prevent a flat roof. Exception possible according to the plan.

Why would anyone willingly build a flat roof?

Because they like it? Because they like it. Why do you have to justify it? But if you want to read an argument beyond personal taste: the roof slopes are omitted.

Also because:

I only know it as expensive and maintenance-intensive.

...which seems to be a myth. At least in our case, it was not more expensive than the alternative pitched roof.

And

But it is so chic! Doesn’t every modern person want to live a bit like Walter Gropius and Mies van der Rohe?

I simply find that inappropriate and unnecessary. The OP seems to like it, so why ridicule it?

Is a flat roof not cheaper at the moment anyway? You don't have to find any wood and no one to put it on for me. Acquaintances in Bavaria built without wood except for the wooden floor, the stairs are concrete, flat roof, no basement.

Why? How does he justify his wish?

Well, essentially it is his frustration over the restrictions in his own house and the fact that now flat roofs are also allowed, which means the restrictions regarding size no longer apply. I would say that a not insignificant amount of envy plays a role here... Unfortunately.

It is common to reinterpret the eaves height as the wall height in a flat-roofed house, which then results in at least a setback recessed upper floor on both eaves sides (or even the reduction of the entire house height).

I don’t need much imagination for this: presumably simply resentment about the fact that at the time of his building, the old regulation still applied. I find the motivation of the OP in favor of flat roofs more interesting.

Exactly. Well, our motivation for flat roofs actually arises from the low eaves height of 3.75 m. With a shed roof, a minimal knee wall would arise on one side; if you place this on the south side, you can put a lot of photovoltaics on the roof but then you no longer have the nice view. The low side in the north means you have the nice view to the south but photovoltaics are no longer sensible. A gable roof results in too many roof slopes and the low knee wall. A flat roof leads to no roof slopes, a great view to the south, and plenty of roof area for photovoltaics.

From the perspective of aiming to create good quality of life in the house through a positive neighborhood relationship or at least not fostering hostility, this question is of interest. Instead of speculating about the neighbor, engaging in conversation and showing appreciation through interest helps, for example, to find common goals (such as a good neighborhood or a generous fence solution, or ...). The irritation caused by the non-fulfillment of a neighborly wish can thus be channeled not into anger but into a feeling of warmth and coziness. :)

That was very important to us from the beginning, which is why we already sought conversation during the planning phase. But if the other party offers "our way or no way," it is of course difficult.

Even though I can understand the frustration, it is good for the future relationship to see the neighbors not as the opposing side but rather as the neighbor side or at worst the side next door...

This was very important to us from the beginning, which is why we already sought the conversation during the planning phase.

Great.

But if the other side offers "Our way or not at all," it is of course difficult.

True. The term "other side" already says a lot. I wish for a smooth construction process and as good a neighborhood as possible. There will continue to be opportunities to reconnect in order to prevent hostility from arising.

We also have such a sweetheart as a neighbor and a friend is currently dealing with a nightmare neighbor as well. The lesson we both learned from it: Focus on yourself and trust that there is sometimes an advantage to the fact that Germany is so eager to regulate. If your flat roof is approved, your neighbor just got unlucky. If it were the other way around and HE was building now, he might also choose the few sloped roofs. If he wants to postpone it and can, but it still gets built, he basically just shot himself in the foot (no more nice neighbors who actually wanted to get to know him openly). In the situation itself, it is very hard not to let it get you down but after a few weeks the whole excitement settles again and maybe your neighbor will also have come to terms with the fact that he now just has another flat roof house next door (really, there are worse things, even if I personally don’t like it visually either) and focuses on the benefits of a nice neighborhood. Much joy (and nerves! :) ) with and for the upcoming construction and never forget, despite the trouble, the joy about your home, which should last the longest :)