This is what my grandmother made to go on biscuits. We never had sausage gravy, but it's exactly the same. Just use the drippings from frying country sausage like Jimmy Dean. I never measure, but I'll give you some guidelines-2 tbls of fat + 2 tbls of flour will thicken 1 Cup of liquid. So for 2 cups of gravy you'll need about 4 tbls of drippings.
4 tbls fat left from frying bacon or fatback or sausages
4 tbls flour or enough to form a thick paste
2 Cups milk
salt & pepper to taste
Over med-high heat cook, stirring constantly, brown the flour in the fat for at least 3 minutes. Reduce the heat and add the milk stirring like mad. Raise the heat and keep stirring, until it comes back up to the boil. If the gravy is too thick, thin it with somemore milk. Turn off and season with salt and pepper. If you're making sausage gravy, crumble one of the sausage patties into the gravy.