|  1 |    initial version    |  
Try the "Merge Spaces from External Model" user script in the SketchUp Plugin. It is demonstrated in this video.. You will have to re-match surfaces after merging geometry from one model to another.
You could also try the Create Baseline Model measure on BCL to create a baseline from your proposed model. We have a video for the baseline measure as well.
    |  2 |    No.2 Revision    |  
Try the "Merge Spaces from External Model" user script in the SketchUp Plugin. It is demonstrated in this video.video. You will have to re-match surfaces after merging geometry from one model to another. 
You could also try the Create Baseline Model measure on BCL to create a baseline from your proposed model. We have a video for the baseline measure as well.