I have what may be a possible bug (or undocumented feature). TFRubies seems to ignore groups when producing it's timber list. Exploding the groups results in the timbers appearing in the list. Which leads to the following request:

Is there a way in which we could mark objects as being timbers? This would allow the creation of complete house models while still being able to produce the timber lists. I'm not sure if this is something that one can do in Sketchup. If I find the time in the near future I can take a look at the tfrubies code and see if I can work it out, but I don't see my spare-time-O-meter being full any time soon.