Roasting Pointers. 1  Temp: Preheat the oven to 450°F. Roasting vegetables in the oven should be done at high heat so they caramelize on the outside.  Pan: A heavy 13x9-inch roasting pan works well for roasting vegetables, but you can also use a large baking pan. To keep cleanup to a minimum, line the pan with foil. Place the vegetables that take the longest to cook in the pan. Do not crowd the vegetables or they will steam instead of roast. If you like, add 1 or 2 heads garlic with the tops trimmed off, several sprigs of thyme, and/or snipped fresh rosemary, oregano, or sage.