I use plastic lidded storage bins, an old repurposed drawer and a covered kitty litter box. An eclectic mix!
None of my nestboxes is permanently affixed, though. I like being able to clean them out frequently because around here we have nestbox mites to worry about, especially in the summer. So I like being able to take my boxes right over to the composter and dump out the shavings. I dust the bottom of the box with poultry dust and add fresh bedding. In the summer, I do this weekly.
I also have two daytime tractors, and I need portable nestboxes to go in there, too. Oh, and one other thing: when I had broody hens, it made it very easy to manage them within the portable nestboxes: I simply moved the hen with her eggs, right inside the box, where I wanted to put her.