I registered 2 draw handlers, one for adding text to the view (2d, POST_PIXEL) and another one for 3d (POST_VIEW).

I draw lines along vertices that I add when I click in the view with the left mouse button and then I use this shape to create a plane from this, a mesh, that you can extrude afterwards.

My previous #Blender addon tutorial can be found here:

I will integrate this functionality into my hardsurface fast carve addon, that can be downloaded here for free, also for Blender 2.8:
https://github.com/jayanam/fast-carve/tree/fast-carve-2-8

See my social profiles here
G+: https://plus.google.com/+JayAnAm
Twitter: https://twitter.com/jayanamgames
Facebook: https://www.facebook.com/jayanamgames
Patreon: https://www.patreon.com/jayanam

Production Music courtesy of Epidemic Sound: http://www.epidemicsound.com