I have made them but I make it ups as I crochet.
Firstly I fold over cut in half edge and zig zag with machine to stop fraying (2 thicknesses)
I then get my crochet cotton and a wool needle and do a row of blanket stitch with 1/2cm (1/4ins(?)) apart, tie off.
With the new peice of cotton I just crochet a row of trebles, then next row a treble in every second stitch and decrease as I work up when I get the length I like.
Then I just decreast to approx 8 (?) stitches doing enough of those rows to make the loop for the rail for the towel to hang over and miss a couple before the last row to pop your button through.
Depends on how good a crocheter you are and how fancy you want to be. I just like basic LOL
Hope some of this made sense,