Hi there, SketchUcation.
I am making layouts for level design purposes (Source engine editing tool "Hammer") and it requires groups of convex/volumetric geometry for it to work. You can't just have flat/2d surfaces and import them in unless they are models (that's a far more complex fashion which eliminates lightmaps, and does not include collision for what I am aiming for and ETC etc)
Here are the processes I am currently thinking about. (If you have any suggestions to make, that's perfect, I seriously doubt my method is the best.)
- Turning all selected faces into groups (Plugin here).
- Edit endless amount of groups at once in one click (plugin needed)
- Backside-extrude all the selected surfaces to create volume (plugin needed)
These 3 steps would ensure that every 2D faces in the Sketchup model would turn into 3D geometry with their own respective group (These groups are later exported into the game in VMF format as working convex geometry.)
It is also important to avoid backfacing.
If you know a plugin that does all of that in one go, linkpls. 
Thanks for your time.