Preheat the oven to 425°F (220°C).
In a large bowl, toss the halved potatoes with 1 tablespoon of olive oil, 1/2 teaspoon of Cajun seasoning, 1/4 teaspoon of smoked paprika, 1/4 teaspoon of garlic powder, 1/4 teaspoon of onion powder, 1/4 teaspoon of salt, and 1/8 teaspoon of black pepper until evenly coated.
Spread the potatoes in a single layer on a large sheet pan and roast in the preheated oven for 15 minutes.
While the potatoes roast, in the same large bowl, combine the corn pieces and sliced smoked sausage with 1 tablespoon of olive oil, 1/2 teaspoon of Cajun seasoning, 1/4 teaspoon of smoked paprika, 1/4 teaspoon of garlic powder, 1/4 teaspoon of onion powder, 1/4 teaspoon of salt, 1/8 teaspoon of black pepper, and 1/4 teaspoon of cayenne pepper. Toss to coat evenly.
After the potatoes have roasted for 15 minutes, remove the sheet pan from the oven and add the corn and sausage mixture, spreading them out evenly around the potatoes.
Return the sheet pan to the oven and roast for an additional 10 minutes.
Meanwhile, in the large bowl, toss the peeled and deveined shrimp with the remaining 1 tablespoon of olive oil, 1 teaspoon of Cajun seasoning, and the remaining 1/4 teaspoon of cayenne pepper.
After the potatoes, corn, and sausage have roasted for 10 minutes, remove the sheet pan from the oven and add the shrimp in a single layer on top of the other ingredients.
Drizzle the melted butter evenly over the shrimp and other ingredients on the pan.
Return the sheet pan to the oven and roast for 5 to 7 minutes, or until the shrimp are pink and opaque and cooked through.
Remove the sheet pan from the oven and sprinkle the chopped fresh parsley over everything.
Serve the shrimp boil immediately with lemon wedges on the side for squeezing.