I make chicken stock pretty much the same way I make my beef stock.
I have roasted 4 chicken carcasses along with 2 carrots and 2 onions, roughly chopped. I keep the skins on the onions as it gives the finished stock a rich colour.
It doesn't matter what vegetables you put in, whatever you have. Sometimes I don't even bother roasting the carcasses or add any vegetables at all. It just makes a straight chicken broth. You can always add spring onions, fresh ginger and sesame oil once the broth is made for the basis for an asian flavoured soup.
Anyway back to this one. Once roasted I put it all in the slow cooker with some celery stalks, celery leaves and also the celery bulb, which has the most flavour and most people throw away. Add about 10 peppercorns 3 or 4 bay leaves and enough water to cover it all. And don't forget some whole garlic cloves. You could also add some fresh herbs like thyme or parsley. I didn't have any today.
I start the slow cooker on high for about 6hrs and then turn to low and continue cooking anywhere up to 12hrs, often overnight, especially if it is a big quantity.
Let it cool down and strain the stock. Taste and season accordingly, don't scrimp or the stock will be bland. The fat settles on the top as you can see. When the stock is at fridge temperature the fat solidifies and makes for easy removal, making your stock fat free. I store some in the freezer in the cleaned milk bottle and the other goes into the fridge ready as the base for some soup. Lily has requested Broccoli and blue cheese soup. Mmm haven't made that one before.