Preheat oven to 450°.
Spread turkey wings and turkey neck on a rack set in a large heavy roasting pan.
Brush with 1 tablespoon vegetable oil; roast until browned, about 1 hour.
Chop carrots, celery stalks, and onions; toss with 1 tablespoon vegetable oil.
Arrange vegetables around turkey parts.
Roast until vegetables brown, about 25 minutes.
Transfer to a large pot.
Add giblets and 1 gallon water.
Bring to a boil, reduce heat to medium-low, and simmer, skimming surface occasionally, for 3 hours.
Strain into another pot; boil until reduced to 2 quarts, about 30 minutes longer.