Do you have a specific type of objects in mind? CAD can do many categories from carpentry over machining to manufacturing.
For 3D printing there are already 2 courses on CGC. Have you checked those?
https://cgcookie.com/courses/make-it-3d-printing-with-blender
https://cgcookie.com/courses/printlab-your-guide-to-3d-printing-with-blender-and-a-prusa-printer
I do own Construction Lines, but haven’t used it in forever. There were a few updates since I last used it. Back then I had a bunch of issues here and there, that I stopped using it.
Precision Drawing Tool is helpful, albeit a tad convoluted for my taste. I only use it in specific cases when I need a precise tangent between two circles for example.
