This sweater with the granny square surprise on the back is worked in two pieces. First, you make the granny square, then you attach the yarn for the front to the top of the square and work your way down.

This video walks you through the steps to make your own sweater. The Knitpicks yardage is estimated and may vary. Any slightly fuzzy fingering yarn should work nicely to get the look. Definitely find something with some drape.