Any thing small that they can get in and hunker down in, they will use it. Small rabbit boxes would be great. Small cat crates, dishpans, etc
Free feeding is good. Some people remove feeders at nite to help reduce attracting mice/rats, etc. Chickens don't eat once they have gone to roost at nite but they do feed shortly before they go to bed to get them thru the nite.
Some people will just feed certain amount in the a.m. and again in the evening. I prefer to free feed and throw treats in am and pm.
They like very small bird seed. I get finch mix.