Yes you should use one nesting box per chicken and I don't know the measurement to mine but you can use anything for a nesting box I know people have used buckets and and cardboard boxes. You can use a milk crate and cut a opening. I added a photo so you can get the idea. Hope i
I think it depends on how big your chickens are for the size. Bantams can have smaller nesting boxes than large hens. So I am thinking 12' x 12' for small birds up to 18" for bigger ones? My neighbors use 5 gallon buckets turned sideways as nesting boxes.