We started putting our babies out at four weeks and still brought them in at night. They started staying out fully at five weeks. It's definitely personal preference though one week might be a tad young.
I have a brooder coop. I put their brooder cage in it with their feed and water and a heat lamp at night. For their first week in their coop I keep the pop door shut. After a week and if the outdoor temp is good I open it and let them go out on their own. Sometimes it will take a few days before one will venture out then eventually the rest will follow.
we do things a bit different here... mine went out into their coop at 3 days, with a heat lamp of course. They've been out there having a ball and we've had no problems, even with the miserable spring we've had. They're 2.5 weeks and loving life... we put the lamp down low and have simply been raising it as they get bigger and the weather improves. The last 2 days we've been able to have the lamp of for the day light hours. hope this helps