You can take any fabric you like, a warm one like fleece or nicky velvet, a cotton or satin one, a coated fabric or waxed canvas, coated canvas to brave the rain! Whatever you like!
The basic dimensions? take an A4 sheet!
You'll also need a cord or lace about 60cm long (depending on the length you want), a second about 30cm long unless, as in the tuto, you're using the rest of the cut-out from the second part, buttons, ribbons, lace, pieces of fabric, etc... in fact anything you need for decoration...