A small/petite sweater takes less than a skein of the color you're using least (ex.) the white in the image above) and about a l lb skein of each of the primary alternating colors (ex.) orange and blue). It's best to use soft yet durable flexible yarn, like organic wool.
Only 2 different stitches are required to make this sweater: HDC (half double crochet) and crochet to finish the edges and connect the granny squares. If you know how to make a granny square (and you can learn from a tutorial posted right here on this blog a few years ago - scroll waaay down), you can make this sweater yourself.