Mine get mixed wheat, barley and triticale. They are free range, and also do well picking up oil seed rape that eggs spilt. Young birds get chick crumb or growers.
I have some birds in a shed. They are young at the moment so get growers, plus grains, but later I will invest in either more growers or layers pellets as they don't have access to all the greens and bugs and dirt that the others do, and it seems doubtful to me that three grains and some oyster she'll give all that a chicken needs to thrive. If there were thick snow for weeks I would also think about pellets for the others on the same basis.