A more detailed explanation of my method follows:
I took the original Sketchup file and created individual files for each thermal zone by deleting the surfaces and subsurfaces not part of the zone space. Then I loaded each zone into Sketchup with the OpenStudio plug in and copied the space elements into a new OpenStudio space as per your instructions then saved it as a unique OpenStudio file. Then using the method shown in the NREL Merge Zones video, I was able to congregate the thermal zones (spaces) to create an model of the entire building into one Openstudio file. What I discovered was that I had to have a unique name for each space, otherwise the Merge file method would replace the existing OpenStudio space.
The method is someone tedious, but the original Sketchup building model, though not large, it had some complex surface elements. So this saved the effort in creating a new model in the OpenStudio plugin from scratch. For simple buildings in the past, I have created the zones using a text editor for the EnergyPlus idf input file.