Preheat oven to 450°.
Arrange chicken in a single layer on a jelly-roll pan coated with cooking spray. Combine onion and next 3 ingredients (through oil) in a bowl; toss well to coat vegetables. Arrange vegetable mixture in a single layer on another jelly-roll pan coated with cooking spray. Roast chicken and vegetables at 450° for 1 hour and 20 minutes or until browned, turning occasionally.
Place wings and vegetables in a stockpot. Pour 1/2 cup water into each baking sheet, scraping to loosen browned bits. Pour water mixture into pot. Add 5 quarts water and remaining ingredients to pot. Place pot over medium-high heat. Bring to a boil. Reduce heat to low, and simmer 4 hours, skimming off and discarding foam as needed.
Strain stock through a fine sieve into a large bowl; discard solids. Cool stock to room temperature. Cover and refrigerate 5 hours or overnight. Skim solidified fat from surface; discard fat.