While helping a client get a new plugin working with Sketchup Make 2016 (which you can get free from here). The plugin was for rendering and the client advised that it was a free plugin that worked with the free version of Sketchup. The plugin can be found here and is simply downloaded for installation.
However a couple of gotcha’s first. If you have Sketchup 2015 or slightly earlier version on your machine the install will actually work for them (but not for Sketchup Make 2016) by placing the plugin in the folder
C:\ProgramData\SketchUp\SketchUp 2015\SketchUp\Plugins
You will find a folder named “ImaginationVisualizer” folder as well as a “ImaginationVisualizer.rb” file.
Copy both to
C:\ProgramData\SketchUp\SketchUp 2016\SketchUp\Plugins (Note if you have no existing plugins you may need to manually create the Plugins folder - I had to)
Then open SU16, go into the Window menu, then Preferences. In the Extension tab, just check the box beside Visualizer and the icon will appear, as well as the Extension menu entry.
That should get you started with Visualizer for Sketchup !!!