This Recipe was taken straight from this link:
"For a gumbo I use about a 1/4 to 1/3 cup of flour per gallon of gumbo. That's just
a general rule of thumb I use to get the consistency I like. Some people like thick
gumbo and some like thin. If in doubt, cook more roux than you think you need
and take some out before you start putting the other stuff together. You can then
add more roux if you want a thicker consistency.
If you are a beginner at rouxs start out with a half flour, half oil mixture. The more
oil you use the less likely it will burn too fast. As you get better at it you can use
less oil. Add the oil and flour to the pot and set the fire on medium. My best rouxs
were made in a cast iron pot or cast iron skillet. Using a spatula, stir the roux
scraping the entire bottom of the pot every time. Using a spatula allows you to
move all of the mixture around and you don't have to make more than a few passes
to do it. Stir the mixture every 15 seconds or so. The roux will bubble at first then
will get smooth as it cooks.
WARNING.. Don't be tempted to walk away and do
something else, if the roux burns at any point during the process, it is no good.
Once the roux has turned a medium brown lower the fire just a little. Keep stirring
as you were before. You will notice with each stirring the roux gets a tiny bit more