making suet for chickens

I wouldn't feed them suet - it is far too fatty not good for them. They are fine with their layers pellets/mash, grit and oyster shell available to them whilst they are awake and mixed corn with some greens as treats. If you want to give them something warm then you can make porridge with water (not milk) or mix their layers pellets/mash with hot water.
Wild birds get fed suet balls as they do not have a regular supply of food and sleep outside. They also use more energy flying round trying to source any food.