Great pattern! All rug patterns I have tried before with super bulky yarn did not lay flat. This one does!!

Modifications:
I used a Q hook and double strands of yarn throughout. (It took about 4.5 skeins. I crochet on the loose side, so if you crochet tighter, you could probably make it with 4 skeins.)
I followed pattern through round 9, then for my last round:
ch 1, sc in next 2 dc, ch 3, sc in next 6 stitches repeat around and instead of ending with 6 sc, end with 3 sc and slip stitch to beg. ch 1. Finish off and weave in ends.
Rug measures 32” across. Takes about 2-2.5 hours to complete.