In a medium saucepan, melt the butter. Add the flour and cook over moderate heat until smooth, about 2 minutes. Strain 3 1/2 cups of the liquid in the roasting pan into the saucepan and whisk to blend. Bring the gravy to a simmer and cook over moderately low heat, whisking occasionally, until slightly thickened, about 5 minutes. Stir in the parsley, sage and thyme and season with salt and pepper. Pour the gravy into a small pitcher. Carve the turkey and serve with the gravy.