With dog coats, don't go for the 'cutesy or fashionable' look. They are a waste of money and or time making them.
He needs a simple coat. You can make one as cheap as chips. Buy a couple of metres of flanalette type material and another thicker material that is more hardy. Find a pattern (again, google is your friend) or have a look at simple coats in the pet store so you get an idea of the shape, and then sew the material together. Add a strap and a button or 2 and your done.