Thank you for your response. I am well aware CA is non-trivial software which requires a serious time investment to learn how to use.
However, it is built for the USA market, and we live in Europe. The defaults are almost 100% non-applicable over here, and require extensive customising.
Whilst I appreciate your comments, I was asking for help wrt _one_ thing: the auto-generated Floor Structure. This problem affects all floors.
Since I posted my original msg, I found a review on Amazon which shed light - to wit, the ability to edit the Floor Structure is disabled in the Home Designer edition. This one piece of info was the lacking piece of the puzzle, ie. it cannot be done without an upgrade. No wonder I couldn't figure out how to do it.
Chief Architect: you should put popup notes on disabled features telling people exactly wtf is going on so they aren't driven nuts.
Another criticism: every single manual, video, etc uses inches - who else does that outside the USA? Updated manuals are defo called for.