Take your chicken(s) and separate into pieces. You'll want to piece out the breasts, thighs, legs, wings into one roasting pan. It's OK (preferable) if you keep the bones in the pieces of chicken you're separating. At the same time, set everything else (the bones and any other scraps) into another roasting pan.
A slight rub of 2tbsp of olive oil on the bones and scraps, and toss into the over under the broiler at "high". Roast for about 30 minutes, and flip the pieces to ensure you're browning up all sides. Keep roasting for another 30 minutes or until the bones and pieces have some good colour on them, however without burning them. You're trying to get as much colour on them as possible.
Heat 2tbsp of olive oil in a deep soup pot and get it ripping hot. While it heats, chop up 2 yellow onions, 1 large carrot (or 2 medium ones), approximately 1/3 of the head of celery in a rough chop along with 4 cloves of garlic and toss in over the oil. You're looking to get some browning on the vegetables, but certainly not burn them. Ideally use a wooden (or plastic) spoon. Add about 1/3 a can of tomato paste and continually mix to coat the vegetables, also bringing out a bit of the sugars in the tomato paste. Be careful not to burn.
Once you've got some browning on the vegetables, toss the browned and roasted bones into the pot with any drippings from the pan. Use 1/2 cup of water into the roasting pan to help scrape the fond (the little bits attached to the pan) off the roasting pan and be sure to include them into the pot (they're the best part). Fill the pot with enough fresh water the cover all items in the pot. Add a bit more water if you wish to bring the pot up to (at max) 3/4 full. Add a handful of thyme and parsley then bring the pot to a boil, and reduce to a simmer - which you'll want to keep it at for approximately an hour.
While your stock is cooking away, you'll want to rub the separated pieces of chicken with about 2tbsp of olive oil and roast on high to get as much colour (but not burnt) on the chicken. You're looking to ensure it's cooked about 3/4 the way through. Once done, set aside and let cool.
As your chicken is roasted and cooled, begin separating it into chunks or shreds to your choosing. Typically I suggest a variety of both chunks of breast meat, and more strips and pieces of thigh and leg meat. Set this aside and cover.
Your stock should be completed by this point. Strain into a large tub or bowl through a sieve and discard your scraps into compost. Set the stock aside.
With your soup pot, add another 3 finely chopped onions, 2 large carrots (4 medium), and the remaining 2/3 of your celery, 4 cloves of garlic along with 2tbsp of olive oil and begin softening the vegetables. Once browned add another 1/3 of your tomato paste and mix to coat your browned vegetables. Continue on a medium heat to slightly brown the tomato paste.
Add a handful of thyme and parsley along with the the entirety of your broth to your pot, bring to a boil, and immediately reduce the heat and let simmer.