The link Mr. Chi posted has some free patterns available on their website. Some of the fabric shops also offer patterns in the pattern books.
I used the jacket pattern off the site above and just modified it some. However, if you don't have a sewing machine, you would need to stick to some really basic patterns with as few seams as possible.
I sewed two little dog vests and i did it all by hand. It really wasn't too difficult. You could always stich on little details... like a pocket etc too. Mine were simple. One was made out of thin cord material and the other was a warm flannel plaid material.