I like this, rather than spending silly amounts of money on nest boxes I can go down to my local homeware shop and just buy some buckets.
One question, do you have anything to stop the buckets from moving around? Is the frame shaped to accept the buckets or do they just sit on a flat shelf and are stable enough like that? I'm in the design stages for a new coop and I'm at the bit I'm thinking about the nesting boxes and this just is too simple to ignore.
I use a variety of buckets even the litter buckets for cats. They are great. I often use rope and or fastening agents to keep them stationary. But the frame does work better. I often squeeze the buckets in spaces so they are side by side and wont move out but that sill need a design small enough to fit the amount you want to place. I also use covered cat litter boxes. Because the design is perfect for a nest but the dimensions vary on size of it. But it is perfect for my large gals and they take full advantage of it. Hope this helps...
The Imp uses a bucket for his nesting box, and he seems to be very happy with it. I would think that you would want to make the buckets so that they can't roll around. I would think the you could use a couple on 1"x2", or any kind of scrap boards that you have laying around would work.
I'm converting half a garden shed into a coop at the moment, I think I'll cut a hole in the bottom of the buckets as they will up against the dividing wall, and then add a hatch on the wall so I can just reach through from our side of the shed through the bottom of the bucket. Less intrusive that way.
Ever so slowly getting there - though I have next week off work to move the project on a huge amount hence lots of research this week.