When I make sawmill I leave about 2T of oil in the fry pan. I add maybe 1/4 cup of flour and stir until combined, browner a bit and looks like paste. I add milk until I get the consistency I want. I also add a little seasoning like a rub mix or just salt and pepper.
I cooked this for the sausage throwdown. It was a real winner at our house.
I use pretty much the same recipe as High Q but omit the salt as most sausage has quite a bit in it. I do go heavy on the pepper and may add a little oil if the sausage doesn't render out enough for the roux.