Knitting a Coat: What Should You Keep in Mind?

Dear users, dear designers,
if you want to knit a coat, what should you pay attention to?

Make sure the yarn isn’t too heavy. Ages ago, I knitted myself a jacket out of ribbon yarn, with a cable and lace pattern.... It looks really great, but it’s impossible to wear. It hangs like a sack—it’s way too heavy for the pattern. It’s such a shame.
  I love cardigans… I’ve knitted quite a few.
Also, always make sure the buttons are the right weight for the yarn, otherwise the button placket will sag unattractively downward…