After seeing this I had to try it out myself!
here is what turned out-i decided to do one side in a vinyl coated pink gingham so that she's stay dry and I could wipe my other dogs drool off her easily (niiiiice. hehe ), the inside is fleece. I've made it that that it is reversible and can be worn either way.
I sort of made a pattern up as I went along. I got a huge piece of paper and, using my dog's measurements, drew out a rouge coat shape and worked from that. I kept trying it on her and adjusting it to size before sewing the actual material one...