Building areas: Enter subcategory or 2nd construction area

It would be desirable to include a sub-category or a second construction area.
Example: We are always building apartment buildings. Here we would not only need the floor in the construction area, e.g. KG, EG, or OG, but also the apartment number.
The problem is that I can't simply enter a construction area with "ground floor_apartment 3", as not all houses have the same number of apartments on the same floor. Sometimes we have 3, other times 4.
Of course you can enter the apartment number in the text, but you can't filter by text in the reports.