Slow cookers are great due to their convenience. You turn them on and walk away. They're not especially sensitive to time, and so you will have your chicken done and hot without much concern about overcooking. What you get is a braised chicken, though, not a roasted one. Roasting by definition is a dry heat method. You do it in an oven or on a rotisserie, not in a pot.
If your oven has a timer, and you're confident you'll be back before the bird burns up, you can use that. Otherwise you have to watch it.
You asked how, though. My favorite way of roasting a chicken is to rinse the bird well inside and out, pat it dry with paper towels, rub oil or butter over its skin, season it inside and out with salt and pepper, put a quartered lemon and a couple of sprigs of rosemary inside it, truss it up, and roast it in a standard oven until it's done, which takes around eighteen minutes per pound. Once it's done, take it out, cover it, and let it rest for a quarter hour before carving it so it will retain its nice juices.
This method is easy as it gets, and it has never failed me. The result is always delicious. I'll try to write up the recipe for you and post it on my Hub page later today.