Absolutely no reason not to use the bones left over from a roasted chicken to make stock with. I used to buy only whole chickens for the house(I love roasted chicken- one of my favorite meals), as a reason to have to regularly break down a whole chicken, and to have bones left over to make stock. Hell, even you made chicken wings... save the bones and blanch them first before they go into the stock and they'll work just fine. Not that I'd do that in the restaurant, though...