Hi Rick,
You hit the nail on the head. Don't always use the same thickness especially for a roof top. Currently I use the the line tool with inference locking but this can be quite annoying after a while and if you have have a shape that kicks back and forth many times then lots of construction lines are needed on the corner sections to work out theses distances. (The image I gave at the top was in it's simplest form, this is obviously extremely simple). You have to try it this way to understand how helpful such a tool would be.
If you try any example like this with inference locking it's VERY easy but also VERY time consuming for something that maybe a Plugin could calculate in a few seconds.
This is a problem a bit like many SU Plugins address i.e "Make group" plugin. In native SU, I can select geometry, make it a group, open the outliner, click on geometry, right click and re-name. All very possible, but with this plugin I can can give it a shortcut key and name it on the fly which makes my workflow so much easier and thats why this and many other such Plugins are great workflow aides.