What you'll need:

1. A piece of stiff, black paper*
2. A compass (for drawing circles, not finding magnetic north)
3. Scissors
4. A hobby ("exacto") knife
5. Some velcro to attach the masks to the step-up ring
6. A pencil
7. A step-up ring (at least 5mm bigger than your filter size)

Total cost: ~$25
* The original author used red paper and ended up with a reddish cast on his images.

In the original article, the author sandwiched the paper mask between filters rather than directly attaching it to the lens. This wisely avoids damaging the lens, but can be a bit of a pain. If you have two clear filters, you can use those as the Korean author did instead of the step-up ring, or you could purchase two cheap UV filters and knock out the glass. The goal is to secure the mask without shooting through low-quality glass.

The Step-up Ring
You can eventually create as many shapes as you'd like, but you'll only need to modify one step-up ring.

Step 1: Cut a Strip of Velcro
Cut a strip of velcro — it doesn't matter whether you use the rough or soft side — so that it's about as thin as the lip on the step-up ring.

Step 2: Attach the Velcro
Cut the velcro strip into small pieces so that you can place them individually on the step-up ring. Cut them short enough so that you can put them on the step-up ring's lip to cover most of the circle's circumference. Attach them to the step-up ring's lip, cutting more strips as needed until you cover the entire ring. This will allow you to attach the mask in whatever orientation you'd like.

The Mask
You can create as many of these as you'd like. Visit the original site for some interesting ideas.

Step 1: Outline the Outer Circle
Set the compass to make a circle just slightly smaller than the step-up ring, mark the center of the circle on the black paper, and draw the circle.

Step 2: Create the Mask Circle
Because the mask must be smaller than your lense's aperture, do some math. If you're going to use a 200mm lens at f/5.6, the aperture will be 35.7mm in diameter (200/5.6), or roughly 1.4 inches. Thus, your shaperture should be smaller than 1.4 inches. This measurement is true whether you're using a cropped-frame or a full-frame camera.

Measure half of your aperture (the radius) on your compass and, using the same centerpoint as before, draw another circle.

Step 3: Draw the Shaperture
Within the circle, draw the shaperture you want to use. Shade the shaperture so that it's easier to see when you cut it in the next step.

Step 4: Cut out the Mask
Cut the outer circle out from the paper.

Step 5: Cut Out the Shaperture
Using your hobby knife, cut the inner shape out from the mask. Make sure to use a cutting surface of some sort, such as an old phone book. Place the knife against a straight edge while cutting to get better cuts.

Step 6: Add Velcro
Using the opposite side of the velcro that you used to make the step-up ring, cut four thin, small pieces of velcro and place them equally around the mask.

Step 7: Attach to the Step-up Ring!
Attach your mask to the step-up ring!