My roadrunners are laying eggs with soft shells. What causes that and how do I rectify it
Its a sign your chickens are lacking calcium in their feed.
You can buy calcium supplements which you can buy from reputable shops. Check Vetco, Farm & City, etc..
Another cheaper option is to roast egg shells a bit and grind them and mix with feed. Eggs shells have high calcium content. If you can find plent egg shells the better, good luck!