How do I create buttons in a UI menu?

I want to create a check button for quarter round on trim (as rooms with carpet don’t need it). I want that button to activate a menu of quarter round styles. I also want to create buttons with various material options ( with pictures of the skp file). How can I do that? Thanks!

Not, unfortunately.

The menus are not as much of a playground as the 3D model where you can create everything you want from edges. What you can create in the UI is limited by what the API provides methods for (and even if more was possible, it is still recommended to follow good practice in “user interface guidelines”).

A menu can contain menu items to which you once assign an unchangeable text and an action (a proc or method). A menu item can also have a state which you can change between enabled and disabled (action not applicable in the current context) and optionally checked and unchecked (checkmark in front of text, probably what you want).
See here:
SketchUp calls the validation proc very frequently (when ever it refreshes the menu), and your validation proc returns what state the menu should show (so you don’t call a method to change the state, but when SketchUp asks, you respond with the state). Ideally this method does not do heavy computation but just returns a variable.