Heat oil in a large skillet or heavy-bottomed pot over medium-high heat. Gradually stir in flour, cooking and stirring constantly until the roux reaches the color of a penny (about 15-20 minutes).
Add thyme, basil, crumbled bay leaf, salt, cayenne pepper, and black pepper to the roux, stirring to combine.
Add diced celery, bell pepper, onion, okra, and minced garlic to the roux mixture. Cook until vegetables are tender, about 20-30 minutes, stirring frequently.
Remove the vegetable and roux mixture from heat and let cool for at least 30 minutes.
In a large soup pot, bring chicken broth, clam juice, and reserved shrimp shells to a boil. Cook for 10 minutes to extract flavor from the shells.
Remove and discard the shrimp shells from the broth using a strainer or slotted spoon.
Stir the cooled vegetable and roux mixture into the seasoned broth. Cook over medium heat until the mixture thickens.
Add fire-roasted tomatoes and all seafood (shrimp, oysters, crabmeat, and crawfish). Simmer for 20-30 minutes, stirring occasionally.
Serve hot over cooked rice and garnish with chopped green onions.