Development plan in NRW - is a attic possible?

I would see it this way now, that only the living area of the attic as well as the top floor must not be larger than two thirds of the living area of the ground floor, right?

Apart from the 3/4 thing, the top floor does not "care" about the ground floor. It is always about the floor directly below! So if the ground floor has 100 sqm, the first floor may still have 75 sqm and the attic may have 75*0.75 sqm = 56.25 sqm. However, if the first floor does not fully use its allowed 75 sqm and is, for example, only 60 sqm, the same attic becomes a full floor!

I believe the OP has a "brother in spirit" in this forum - I guess there is a similarly conceived basic crazy idea behind his forehead as in this thread:

Wir wollen durch Erker die Fläche im EG so erhöhen, dass die Flächen im DG unter den Schrägen möglichst klein werden (Hessen; DG Max. 75% des EG mit Höhe >2,3m Rohfussboden bis Oberseite Dachkonstruktion).