Dog coats can be fashionable as well as practical. Although dogs don't necessarily love wearing clothes, it is very important that your dog is protected against the harsh elements such as snow and rain. Making your own dog coat pattern gives you the freedom to make your dog's coat as unique to him and your personality as you wish.
Measure your dog. Decide if you want to include a hood or not. If you are including a hood or attached head covering, measure your dog from the top of his head to right before his tail. Measure him from shoulder to paw on the front two paws, if you're including sleeves. Measure the girth of his front legs (at the part nearest to his body). Have him lay on his back or side and measure from his collar (under his chin) to right before his crotch (so he will be able to urinate in the coat). Measure your dog's girth at the widest portion of his body.
Design your dog coat. You can include sleeves, but they're not necessarily more practical for keeping the dog's body insulated. Make sure your coat does not cover his genitals or behind so he can still eliminate waste when wearing his coat. Draw the coat from several angles so you can get an idea of what you're making. Most dog coats stop on his back right before his tail and come inward to cut right above before his genitals, leaving his hind legs exposed.
Using the measurements you have taken, draw "panels" for the dog coat. The coat is easiest drawn in two parts. Draw the left side of your dog coat first, holding it up to him as you draw to make sure your renderings are accurate. Draw the right side following. You do not need to include holes for the paws in the pattern, as you can cut those out of the fabric later.
Design your sleeves. Figure out where they will go on your pattern and how long you should make them. Cut these out separately. Make each with one rectangular pattern that you can sew together to form a cylinder. If you wish, you can do two smaller rectangles to sew together to make a larger cylinder.
Cut out your pattern. Hold the pattern up to the dog again to make sure it fits. At this point, you can cut paw holes, or you can wait to do so in your fabric.
Pin your pattern to your fabric and begin your project.