I have been following the guides for the cutNFill instructions on the Sketchup Forum as well as Sketucation. I am facing the same issue as @podanyc (Cut N Fill Plugin - Mesh / Solid Errors & Best Practices)
I tried scaling the group and using the plugin. However I could not achieve the result and it still shows 0.00 cu.ft.
I understand that the mesh needs to be simplified.
Hoping you would be able to take a quick look at the file attached and give any guidance on how to avoid these issues.