I have traced round the architects plans in AutoCAD to create a very basic single plan then extruded the rooms or zones to the given heights and then imported the DWG into Sketchup and it works quite well.
I did try the separate room situation first (i.e., using wall thicknesses) but VE got confused with floor levels in that instance.
The best source of info I could find for the VE plug-in is actually the help button on the VE plug-in toolbar (highlighted in the screen shot) as it gives you some more info instead of the pdf available from the site.
Hope this helps..... and I hope I am going in the right direction too...!!

