The pan drippings will probably have too much fat. You shouldn't need more than about a quarter cup. Carefully pour off the excess fat, so as not to lose the flavorful juices. Mix up about a half cup of flour with about a cup of water to add to the drippings. Also, have ready about 2 cups of water and a can of chicken broth. Add the flour and water mixture over heat, stirring to loosen stuck on bits, then as the mixture will start to thicken quickly, pour in the water and stir and continue to loosen any bits still on the roasting pan. Let gravy simmer for a little while and add chicken broth and/or water to the desired consistency. Now pour through strainer into a large saucepan, taste and adjust seasoning. If it's not thick enough, make up some more flour and water, pour through a strainer and stir and simmer. This should yield 3 - 4 cups of gravy. Adjust quantities for a really large turkey.