Carefully remove turkey from the pan and place on platter. (use a large, heavy spatula under back side with a large metal spoon in the cavity to lift,) Let the juices drain off turkey into turkey roasting pan as you transfer. Hopefully you have a nice collection of juice.
In a separate bowl, mix 1/2 cup of flour slowly adding 1-1/2 cups cold water, whisking until smooth. Depending on the size of turkey and amount of juice you might not need it all. You might need to make a bit more. Heat the juices and slowly add less than half of the flour/water mixture. Keep whisking the gravy over medium heat until it begins to thicken. Let mixture lightly boil while stirring constantly. If gravy is not thick enough, add a little more of the flour mixture until you reach desired consistency. Add salt and pepper to taste. If it is too thick you can add more water. Add chicken broth if it needs more flavor.