I made Stuart a coat. We live on the West Coast of Canada and it can be rainy in the winter. I wanted to make sure his tummy was completely covered because I want to keep road-grime splashing up from his feet. He is white, and his belly gets really dirty if the roads are wet. I make my own patterns, but basically the design covers him from neck to tail, fastens around his chest, and fastens under his belly. I custom draw the pattern and measured between his front and back legs to get the exact width the fabric needs to cover, so no belly is exposed (except he is a male so I had to make allowances for certain parts of his body that stick out down there...)
I use a special fabric made by Polartec, it's called Powershield. Its quite expensive but is intended to technical outerwear (people jackets). It is very stretchy (both ways), lightweight and breathable so he doesn't get hot, extremely water and wind repellent, and of course washable. I put reflective tape on the outside. He has one in blue, one in orange, and one in red. I would love to make him a plaid coat (he is a Westie, so a Scottish tartan would be cute) however Powershield is very hard to get in the first place, and it sure isn't available in plaid. I wont work with cheap fabrics and I want it to be waterrepellent.