If you are making those measurements for take-offs, use one of the cutlist extensions.
If I just want to see the dimensions of an object for reference I use an ancient old plugin called Get Dimensions. With a keyboard shortcut assigned it’s quick and easy to get the dimnsions of the bounding box.
There’s a revised copy of it here:
https://forums.sketchup.com/t/modify-multiple-components/62941/4