Remove all of the meat from the rotisserie chicken and set it aside. (I usually shred it and refrigerate it in a tupperware. I typically only use half of the meat from one chicken for this soup. With the rest of the meat you could make one of these recipes.
Place the entire remaining chicken carcass (the skin and bones) into a large stockpot. Add carrots, celery, onion, bay leaves, peppercorns, rosemary, thyme and water to the pot.
Slowly bring to a boil over medium heat. Skim off any foam that rises to the surface.
Reduce heat to low, cover and simmer on low for 2-4 hours.
Strain broth through a fine sieve strainer, discarding bones, vegetables and seasonings so that you are only left with the clear smooth broth. Stir in chicken bullion.
At this point, you can return the broth to the pot and continue making your chicken noodle soup, OR:
Cover and refrigerate the broth for several hours or overnight. This helps any fat to rise to the surface. Once cooled, you can skim off the thin layer of fat from the top of the broth.
You can refrigerate the broth for several days if you want, or pour it into a large freezer ziplock bag and freeze it for later. If you want to prepare this soup all in the same day, then I suggest making the broth in the morning, refrigerate it, and finish the soup around dinnertime.