Hello frow.gif and Welcome To BYC! Time to start building the coop now, depending on the weather, most people put their chicks outside at about six weeks when they are fully feathered and don't need extra heat anymore. As mentioned,if you let them roam, you will lose some to predators sooner or later, most people have a secure coop and run because of that.
you might like to check out the BYC Learning Center, lots of good articles on all aspects of chicken keeping. https://www.backyardchickens.com/atype/1/Learning_Center