Hens laying eggs on roost

[Pork Pie]

please help
I have 3 lovely chickens
I have made them a lovely secure sizeable run and I have made a new coop with perch and external nesting box.
1. They sleep on a ladder in the run in all weathers
2. They used to lay eggs in box
3. I changed bedding( shavings under perch and straw in box and they now decide to lay by their water feeder!!!!
Any help would be great
I guess it's not a prob really but don't understand!!!

Hi and welcome to BYC.

Did you keep the chickens in lockdown in the coop? If you keep them locked in the coop (with food and water, of course) for 3-4 days then they should associate it with "home". During that time, they will need to lay, and should do so in the nesting box. You can put a couple of eggs in the box to encourage them to use it. Also, putting a flashlight in the coop will encourage them to use the coop, come dusk (you can turn it off, once they are in). I'd also go back to whatever bedding you were using the past.