Well, one rule I like to follow is that they have to be fully feathered before they get to live outside permanently. Usually, the weather is getting nice out and then I take them out in the evenings and let them play in the grass a bit in a bottomless playpen type device I made. So they get to be outside with my supervision, of course......I do this when it's nice out and then finally, when the weather is in the upper 60s, I will put them out in their enclosed chicken run......They usually like it alot, and then at night I have to go out and get them and put them into their coop and shut the door....I have to do this for a few weeks and then suddenly, they get the idea on their own......
I do think their feathering is the first requirement, then the weather is the next.........