I buy it when possible. When the ingredients are friendly. But I usually buy a whole organic chicken and cook it in the rotiserrie. You can cook it any way you'd like. When you're done picking at it like a vulture you can put some aside to make soup afterwards but for the stock just cover the carcass with water in a pot, spice it, maybe 2-3 bay leaves and let it come to a boil then simmer for a good 2 hours. Some add diced up veggies to this which they later discard but I only add veggies afterwards so that they are in the final soup and I can eat them instead of throwing them away. Just strain the liquid into a big bowl. Voila, you have chicken stock. To make soup I usually add 1:1 stock & water.