I a previous post I mentioned that I found a rain coat pattern for Barbie. I have made that raincoat. I don't own a Barbie doll, but I have made this doll I made a while back:
So here is how the coat turned out
The coat is cute, but the upper part of the coat turned out to big for my doll. It may be because I chose the wrong yarn or hook size. It could be that my doll is not a Barbie doll.
Overall the coat looks like it could keep my doll nice and toasty warm.