Christian,
Glad u found archicad-talk!
As with everything ArchiCAD, there is never only one way to do it.
Layers combos, and Views do a good job for this. Something else you might find useful in combination with these is Model View Options and of course with the display order tool you can make things display on top or below.
I show walls as solid lines below the floor framing and dashed lines for the walls above.
Attached is a bad example but you can get the idea.
The fill consolidation tool helps to do this with out too much effort.
Make a copy of your walls and explode it. Delete everything except the fills and use the fill consolidation tool to make a single fill out of that which you can use for walls in what ever view you need it.
Sometimes there is an advantages to doing this over trying to make a fancy assembly of drawings for the layout book.
You can make these wall fills as poche or empty and with what ever border lines you need. They are also quite easy to stretch around to match walls you might move around. The red dashed lines of the floor above that you see in this drawing are actually just a fill.
I like to show the plumbing as well as the walls above on the floor framing plan.
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