I always prefer to work from someone else's patterns. I was running out of time, and this one was a great idea, but would have taken too long.
This was written specifically for Roxy, a 6-pound Yorkie mix. I used Red Heart Christmas yarn--red with gold.
I didn't write down everything exactly, but this is pretty close to what I did. (I guess you could call this an Elizabeth Zimmerman type pattern...even though I don't like her style).
Cast on 16 stitches and make 1.5 inches of K2, P2 ribbing.
Then: increase 1 stitch for the next 10 rows.
Garter stitch until you are 2.5 inches from the full length. (Roxy's version is 16-18 inches total).
Then decrease 1 stitch for the next 10 rows.
Then K2, P2 for 1.5 inches.
Sew up the ribbing + a couple of rows of garter stitches on each side. Put on dog, and see how long it lasts!
Adapt this to your dog/any yarn:
measure around the dog's lower front leg--this gives you the width of the bottom of the shrug
measure from the dog's lower leg, across back to similar place on other front leg--this gives you the total length