My girls are about 6weeks old and I just put them out in the coop. I added a small run it surrounds two sides of the coop (which is 5'x5') and sticks out from the coop about 3ft in each direction (if that all makes any sense, lol), about 3ft high with chickenwire on sides and top. I figure that will double as a safe place for all 4 chickens to be housed if I need to leave for a weekend, etc. My coop has two doors... one to the outside and one to the run. I divided my coop down the middle with some plastic lattice when I put the babes in there cuz the hens weren't too ecstatic about the idea. So the hens (right now) have free-range access while the babes only have access to half the coop & the secure run.
Don't count on them going back inside on their own at first. When I built the run, I figured I'd probably not need to get into it, so didn't leave any openings. Oops. The first night I had to tear the wire off and pick up BOTH chicks who decided to huddle in a corner rather than going back inside where the light & heat was. Second, third and 4th night, one of the chicks continued to stay outside. I think she's FINALLY figured it out though.
I live in the city and "free range" to me means they are roaming loose in my huge yard (triple lot). I have a 4ft chain link fence, which many said wouldn't be high enough, but my hens have never attempted to leave, so it works for me. In any case, you definitely want some sort of secure roosting area (coop or otherwise) to protect from predators (boy are they STUPID once the lights go out... they go practically unconscious!) and also so that you'll know where to look for eggs... unless you want everyday to be Easter! LOL