My iPad case doesn't have an Apple Pencil holder. I browsed Amazon in search for something. I didn't find anything I liked enough to buy, but I saw a model made of elastic that looked easy enough to create. It's supposed to sit on the front cover of the iPad.
I bought a meter of 30 millimeter wide, black elastic and went to my sister. Her specialty is sewing clothes but I figured this would be well within her area of expertise. It took her two minutes once I had told her what I wanted. The result was perfect.
This is how to make the Apple Pencil holder:
1. Measure your iPad cover
Since the holder is supposed to sit on your iPad front cover, you have to measure the height of the iPad in portrait mode. Or you can just go to Apples website and look up the measurements (250,6 mm for iPad Pro 10.5 and 305.7 mm for iPad Pro 12.9).
The elastic should reach all the way around the front cover flap + the length of Apple Pencil (175.7 mm). But it should not sit too loose so subtract a couple of centimeters from the total length. For iPad Pro 10.5 I found 240 x 2 + 180 = 660 millimeter to be a good length.
2. Cut the elastic
Yes, cut it at the right length.
3. Zigzag stitch the elastic ends
You don't want them to fray so zigzag stitch the ends of the elastic. I recommend a tight zigzag.
4. Fold and sew the elastic
Make a ring of the elastic with 180 millimeter overlap of the ends. Attach them with pins if you are not sure you can hold them in place while sewing.
Flatten the elastic ring and lay it on the iPad cover to make sure that it is the right size. It should be about a centimeter short so the elastic fits snugly and doesn't fall off.
If you are satisfied with the fit its time to sew. Use tight zigzag again and sew the sides of the elastic ends together. One seam along each side (= 2 zigzag seams). Make sure to maintain the ring shape so that you don't accidentally sew more than the two pinned elastic layers.
5. You are done
Yay, you have made your own holder for Apple Pencil! Slide it over the front flap of your iPad cover to make sure it's perfect. If it's not, throw it away and go back to step 1. Read the instruction more carefully this time.