This is a sweater for Sencha, a neighbor's dog. I didn't use any specific dog sweater pattern, but I sort of made up my pattern after looking at a few of them. I knit the sweater as two pieces, and then sewed up the side seams, leaving two holes for the forelegs. The neck and bottom hems have ribbing. The rest is stockinette, but as with all knitwear, one can customize this by putting some sort of stitch pattern on the back.
Below is a very rough schematic. I left out any measurements, since this needs to be customized to fit. I think this style will work for your basic tube-shaped dog, and I made the front and back pieces the same width. For the dogs with deeper chests, I think you might need to make a wider front, or perhaps a front that has more increases towards the middle and then decreases back down at the bottom. Or even better, maybe some short row shaping would do the trick for a deep-chested dog. Also, this sort of leg hole might not work if the dog has long legs since it would be hard to get the legs through.