Preheat oven to 400 degrees. On a large baking sheet, place the beef bones and roast until brown, approximately 25 minutes. Turn the bones over and add the carrots, onion, and celery to the pan. Roast for another 25 minutes. Remove from the oven.
Place a large stockpot on the stove and add all the bones, roasted vegetables, thyme, tomatoes, parsley, and some black peppercorns. Cover the bones with water, about a gallon or so. Bring the pot to a boil and then reduce the heat to a simmer. Simmer for 4-6 hours. The longer you simmer, the richer the broth will become. If the water level drops, and the bones start to be exposed, just add more water so that they remain covered the whole time. Strain the broth and skim off any fat. If storing, always allow your broth to cool before you put it into the refrigerator or freezer.