after roasting a chicken is it bennifical to roast the bones prior to making a stock

Definitely not.
Chicken stock is a "white" stock, used as a base for soups and sauces etc.
Beef stock is a "brown" stock, used in different applications.
Picture a Rice Pilaf or Greek potatoes using "off color cooking liquid?

I've never done this. In roasting the bones you may also cook off a lot of the fatty & meaty goodness that's left over from the first round of roasting. You want that flavor in your stock! If you're worried about a lot of small pieces breaking off & floating around in your stock, use cheesecloth to strain it all out once the stock is done (this will also take out a significant amount of the fat).

It isn't necessary, the bones were already roasted with the chicken and have absorbed flavor to impart to the broth that way.