According to the floor area ratio, only 138 m² is possible - 2 floors - Help :)

I have Plan B

Then please confirm that it is definitely not a confusion with the floor area ratio. The neighbors to the north certainly exceed both. I also suspect three other properties. I would therefore give a good chance to a waiver. It is best to post the image and text of the development plan here.

there is nothing mentioned about that

Addition of living rooms on other floors would be standard anyway according to the Building Use Ordinance 1962/1968.

cubist building forms

With existing basement dimensions, slightly changed existing floor plan, and setback floor, I even see good solution options without a waiver. However, in your own quote in #2 it says "children" - plural - how many are they supposed to be?

covered terraces

Little use, bad for the floor area ratio. The roofing should be postponed to a time after the building acceptance.

A child ;)

Here is an excerpt

Here is some more information

...... deleted

Sorry, the legend wasn’t there yet ;)

... I am looking for inspirations and experiences - because I don't want to be completely unprepared - the appointment is only in 14 days

Then take a look at houses and catalogs. 2 children's rooms, bedroom upstairs, downstairs living on 140 sqm is not exotic at first