Bungalow with special development plan ... more ideas?

Possibly the children's rooms and the living room could have a gallery above the ancillary rooms such as building services, storage room, guest room, etc. I just fear that it will be quite costly. Either the bungalow has two different ceiling heights - will that be approved? From the outside, it looks like an undesired stepped floor. Or all rooms get high ceilings. In the living-dining room certainly great, in the 12 sqm bathroom or even in the dressing room oppressive.

Unfortunately, it is still not clear to me how a gallery above the other ground floor rooms should not be considered a second or mezzanine floor.

You sometimes have the sleeping area on a mezzanine in children's rooms, for example, without standing height, accessed within the room itself. Skillfully arranged, I can well imagine that building services and the like are hidden underneath.

For example, in children's rooms you sometimes have the sleeping area on a mezzanine, without headroom, accessed within the room itself

But I don't think that's what the OP means, right?

If arranged cleverly, I can imagine that building services and such could be hidden underneath

I really can't imagine that at all. I wouldn't build an expensive mezzanine without headroom just to house the technology there. I'd rather have a partial basement with comfortable standard height for that. Or am I missing something here?

Why make it simple when it can be complicated? Just do what the [Bebauungsplan] wants.

You can build a nice bungalow on the 500m².

What does "existing terrain 10cm above reference level" mean?

The 5.50m refers to the nearest reference point of the adjacent traffic area, in your case 65.40m. According to the existing heights in the development plan, the terrain rises slightly, which I estimated at about 3%. Depending on the house position on the plot, the maximum height above ground level at the building is therefore reduced again by 10-20cm. From my point of view, the 5.50m simply is not enough for two levels. But I am not a designer. Maybe such a person has great ideas. Report back from the initial meeting once you have found a planner.