Well, I’ve investigated a few more options including the ones from DaveR.
TIG Component reporter does a nice job of it exporting material area (including default) for each component to csv. It does work with a selection, but I have to convert that output to metres from mm (or change model info). Not the end of the world but it works pretty well.
Eneroth material area counter gives a quick calculation of all the material area (including default) in the model within SketchUp. The result is double the figure I would be looking for as it appears to count the front and back faces. There can be no “selection” to choose from however, as it counts all of the material in the model as it is. Again, the units are reported in model units, not the metres I would like.
Two nice extensions, but then I accidentally fell upon “Report on Areas” part of Fredo Tools
It works with selections, the units and decimal separator can also be chosen to fine tune the output within SketchUp which can be exported to CSV.
The selection can be a choice of three ways, by material, by layers or by container which also reports individual areas of components within the selection as well as the total area…
Or simply “by material” for the current selection for a quick total works nicely…
With the units conversion and the versatility on the whole, this is the best (for me at least) I have come across so far.