How long do I roast a 4lb chicken for?

I would roast it at around 325 or 350 for about 1.5 hours, then use a thermometer to be sure it is done. A lower temperature is better, if you cook it at a higher temp it will have a larger chance of turning out rubbery and tough. Low and slow is the way to go, it will always turn out better if you follow this rule.

there are several ways to check for doneness: an instant-read thermometer (test in more than one place--from experience!) should read 165º (some say 170); pierce with a skewer in breast meat to see if juices run clear/yellowish, no trace of pink; jiggle the legs, should be a little loose; and my favorite: lift carefully w/tongs to allow juices to drain in the pan. If they are still pink, roast longer. Having roasted my way through many chickens (about 1 per week), I usually run more than one test and the last really works well--for me anyway.

I generally roast at 425 for between 50-60 mins. And then let it rest for 15 mins