I use covered cat litter boxes. Won't use anything else. Easy to clean, move around- can't be beat for moving broody hens! Simply lift box and move.... No fuss or fighting with angry hen or worrying moved hen will reject new nest box cuz it is 'different' etc.
I always shovel in dirt in the boxes to both weigh them down and prevent the hens from scratching all the way to bottom and breaking eggs on the hard bottom. Many hens will adjust the soil and bedding(usually stems from hay or just pulled up weed-grasses) to make a neat nest, excellent for setting hens.
It is best to have them in the coop 'permanently' so they don't spook at them.. but they will lay in them once they are comfortable with them. Put in eggs, or better, fake eggs or golf balls to make them more appealing to hens ready to lay.