I have looked at SketchUp in the past - even downloaded a Trial version - but I found it difficult to get into.
I'm almost certainly asking too much I suppose. Most of these programs seem to be able to do amazing things and I'm coming at them as an absolute beginner so I must expect a steep learning curve.
I've also found QCAD, which looks rather similar to Inkscape. QCAD has a Users' Forum, where I have learned the simple fact, in answer to my query as to why I couldn't find a scaling tool, that:
"In CAD you always construct in real sizes (1:1). Even if your drawing is several meters in size"This answer alone has saved me much frustration, looking for something that doesn't exist! But it illustrates a commonly encountered frustration - the people writing the Help/Manuals don't appreciate how much we newbies DON'T know and omit to state the basic stuff that they assume everyone is aware of!
Since first posting, I have played about and managed to resurrect my aged copy of Visio. I used to know my way around this, to a basic level of competence, but even here, I'm having to relearn quite a bit, so sadly I have to conclude that the problem is more my own inadequacies than with the software!