You need 2 colors of yarn for this pattern.
The size is totally up to you, because you can choose how many repeats you want to do, and in consequence how wide your scarf will be.
The scarf in the photos kindly offered by Ortenema from his project consists of 4 repeats of the pattern and at his gauge it is 6” wide. And 1 skein of yarn of each color should be enough. So if you want the same width you have to cast-on 29 stitches and do 4 repeats of the pattern. If you want a wider scarf, cast-on 35/41/47 or more stitches (a multiple of 6 + 5 sts).