Prepare all ingredients first - chop vegetables, slice sausage, debone and shred chicken but save the skin and bones in a bowl. Put all prepped ingredients in the refrigerator.
Off to the side, heat a large pot and over medium-low heat, add the chicken stock as well as the skin and bones from the chicken. Cover and warm until needed.
Roux Note: Times will vary on how long it takes to get the roux to a chocolate color, but I am more of a fan of a quick roux, meaning that I use higher heat. It's a little more likely to burn so once you turn the heat up, you have to babysit the pot.
In the main large pot over medium-low heat, add the vegetable oil and the flour. Begin stirring regularly until smooth and consistent. After it is smooth, turn up the heat incrementally to about medium or even a little higher if you are experienced at it. Stir consistently for about 45 minutes to 1 hour.
While the roux is making (don't forget about stirring), separate the chicken bones from the stock by pouring through a fine mesh sieve into a large bowl. Add the stock back to the pot, cover, and let simmer.
In another pot off to the side over medium heat, sear the sausage. Once they have browned a little, remove the sausage to a plate. Add about ½ cup chicken stock to that pan and scrape with a wooden spatula to loosen up any bits from the pan. Pour the liquid back into the stock pot through a mesh sieve.
Once the roux has reached a rich brown chocolate color, add the onion, celery, bell pepper, and garlic and cook for another 10 minutes, stirring very often. The roux will continue to darken to a dark brown color.
Add the seasonings (thyme, paprika, onion powder, garlic powder, bay leaves, cayenne, salt and pepper).
Skim any fat off the top of the chicken stock. Ladle 1 cup of chicken stock into the roux and stir. Repeat until you get a smooth and creamy mixture sort of like chunky gravy, then add all of the remaining stock in.
Add the sausage. Bring to a boil, cover, lower to a simmering heat (low to medium low), and cook for 1.5 hour.
After 1.5 hour, remove the bay leaves and taste test. Add the chicken and turn up the heat to bring back to a simmer. Adjust the heat to maintain a simmer for another 30 minutes. Cook the rice according to package directions before the time is up.
At the end, turn off the heat, and add 1 cups ice cold water. Doing this at the end shocks the gumbo and produces a melded flavor more similar to next-day gumbo, which has better melded spices.
Serve immediately with rice and green onions, and hot sauce.