With the way chicken poo is corrosive and messy and how cracked eggs can stick. Finding these old Metal nest boxes are the way to go. It takes a few decades to get corroded. Wood nest boxes rot in a year. With this pressure washing cleans it like new. 15 capacity is more than enough for 100 hens.... Sometimes 2 hens will be in the same slot.
Keep an eye out on the internet, craigslist, and local ads for this gem. These are not made anymore, but they should be!
Make sure you put straw or bedding of some sort in, the eggs will break on the metal. Nest pads might work. The back end of the nesting box is fully exposed.
The roost can be folded up at night to try and prevent hens from sleeping in the nests.