*APPLAUSE!* A truly clever design! Because the lids snap on tight there shouldn't be a problem with predators and especially so since you'll have collected the eggs by nightfall when most egg-eaters would be prowling around. And when you get the opportunity perhaps you can contrive some sort of wood framing around it or some other way to secure them from wind, that way you won't have to keep removing & replacing bricks every time you need to access the inside. Having them on the outside of the pen also means that your birds have more real estate in their pen to scratch & peck & poop. You may also want to secure any sharp edges of the wire fencing inside the boxes with duct tape so a hen won't injure herself. A few drain holes could be drilled on the bottom in case rain gets in, also so you can hose them out periodically.
Thank you for sharing, I will use your design for my next chicken pen!

DH picked up an old dresser tossed to the curb. Pulled out the drawers, cut the legs off. Mounted it on the barn wall. Put in wood partitions where the drawers were. One dresser now has 6 nesting boxes. Put in fresh hay, and viola, hens wait in line to take their turn. Now we're looking for discarded dresser #2!!! - Ellen

Great ideas! I have a row of six lockers from the elementary school I attended 30 years ago. I've set it up horizontally with the doors opening down.

Need a recipe for the dangerous rooster?

Oh, that roo! We like having him because he's gorgeous, huge and irridescent black with gold saddle and hackle feathers, and once a year one hen gets broody and raises some chicks.

Now if he tries to attack, I grab him around the neck with that grabber and let him struggle. After a minute or so, he gets tired and sits down. I hold him there for a while.

After one of those sessions, he'll ignore me for a week or more.

Recipe for dealing with an aggressive rooster: carry around a large rectangle of chicken wire and walk with it around you into the pen. Worked like a CHARM whenever I went into the neighbors pen to play with the chickens.

plastic milk crates work great