I am also having this problem and am also on a Mac. The main panel simply will not show on my computer screen. This plugin worked well for several months before the main panel disappeared. I have also uninstalled and reinstalled the plugin. Near as I can tell, the panel "thinks" it is showing properly. The Mac version of Sketchup doesn't have any kind of "show all panels onscreen" sort of command.

Layers Panel was a very useful plug-in while it worked. If anyone has a suggestion for fixing this problem, pleas post it.

Yes, that would be helpful for me! Would it display the measurements automatically? Or by selecting? Heights would be helpful too, although widths are most important.

The 1.0.21 update of Cab Maker is working well on my Mac running El Capitan and SU-2016.
Cab Maker is such a useful plug-in! It's a real timesaver in my kitchen design/space planning business.

I'm looking forward to seeing your continued improvements such as face frames, (and I hope) double top drawers for wide cabinets, and end angle cabinets!