Does Sketchup go have an extension warehouse, I want to make cut lists for furniture I’m making
No. Web versions of SketchUp don’t support extensions.
Anssi is correct, SketchUp Go does not support any extensions.
You might want to have a look at upgrading to SketchUp Pro in addition to being able to use extensions for cutlists and other tasks, you would also have LayOut which is great for making documentation for your furniture. You can do everything from proposals to share with the client to creating shop drawings and full size patterns that can be printed on large sheets to make templates from.