So much advice. It's really an easy thing to cook. Oil or butter it or not. Salt and pepper it. Use dried herbs on it or fresh and put some inside it or not. Put lemon, onion, and garlic inside it or not. Truss it or not.
Now - put it in the oven. Use high heat at first (450 to 475) for perhaps 15 to 30 minutes and then drop heat to 350 or so if you want a crisp skin. OR cook lower - 350 or so whole time.
It will be done when thighs and legs wiggle really easily and juices run clear if you prick the thigh with a knife OR if you have a meat thermometer, when the thigh meat registers 165 degrees in the thickest part. Time will differ based on heat you choose. Start checking at about an hour.
After its cooked, cover loosely with foil and jet rest for 20 to 15 minutes. (If you turn it breast side down when resting the breast will be even juicier.)