Step 1: Design!
Here's the basics!
(1) Make a box the size of your ruler.
(2) Set your origin point at the corner of your ruler-box -- now your ruler starts at zero on Illustrator's rulers.
(3) Draw a line, and position it at the 1-inch mark.
(4) Using the Move dialogue box, make a copy of that line 1-inch over (i.e., at the 2-inch mark).
(5) Go back and click Copy instead of OK -- don't sweat it: I made the same mistake a few hundred times.
(5) Use the Transform Again command to repeatedly make a copy of the line 1-inch farther over.
(6) Do that same thing for 1/2-inch marks, 1/4-inch marks, and so on -- or until you lose your mind.
Step 2: Scavenge!
Or, fine, I guess you could go buy some wood at the store. Take your private jet, Rockerfeller.
Step 3: Lazor!
By which I mean: operate the laser-cutter so that you wind up with a finished ruler. Remember to set the outside edge of the ruler to a 0.001" stroke-weight to make it cut the vector.
Step 4: Et Voila!