Check the size of the bird before purchasing. You don't need a giant one as it will take longer to cook! 3 1/2 to 4 1/2 lbs is plenty and cooks beautifully.
Roasted chicken can look perfectly brown on the outside and still be under cooked on the inside. Don't just rely on the color of the chicken to tell you if it's fully cooked. I typically purchase a chicken that's 4 1/2 lbs and it takes an hour and a half or close to it. If your chicken is 3 1/2 to 4 lbs you may find that it's done in an hour. The way to know for sure that your chicken is done is to use a meat thermometer and confirm that the thickest part is 165 degrees.