Few people have asked how I do this and what I use.
I use a black art pen fine 0.4 ($4.95), this time a 3h pencil ($1), basic ruler, soft rubber and a A5 drawing book $2.50).
Draw the basic outline, filling in ruff draft of the zentangle patterns I want to use
Go over designs with the black pen, rub out pencil marks. Then adding further details. End result took me awhile on this one due to being new to using complete free hand instead of templates. Toke approx an hour. Got my inspiration from Google searches