re: How much Roux?

My 12 qt cast iron pot requires a 1-1/2 cup fat to approx 1 2/3 cup flour, maybe a tbsp or so more flour as my measurements are not exact. Cook until roux is dark chocolate colored. After veggies, sausage and poultry added back I top off with stock that is rendered from smoked carcass. I've never actually measured the amount of liquid, just top off until pot is almost full.