I bought a roll away nest box for just the same reason, I installed it in the run but they refused to use it, so I rejigged the house & have managed to fit it in there for the time being. It’s taken about 7 weeks for them to start to use it. The hens are now using it every day, regardless that there is just the plastic mat in there, I did put sawdust in the covered egg collection area as I had a couple of cracked eggs, that seems to have worked. I’m working towards taking the house away as they are in a covered run, but first I need to make it less draughty, then I will reinstall the roll away nest box into the run.