Like one can see on one of the photos I simply crocheted a long stripe with sc stitches and sewed it at the end around an elastic ring. These rings, at least in North Italy, can be found in little jewelry shops.
(Maybe also in other places.)
Note: if I do not mistake, from the second row on, to obtain that ribble effect, I crocheted the single crochet in the back loop.
Note: to have enough crochet-material to cover the elastic ring, however, it will be better to make the crochet piece about 2 of 3 centimeters longer that the cm. surrounding lenght of the ring.
Best will be to crochet a piece, to fix it with pins around the ring and see if the crochetwork will be great enough.