Check out my Mud Eradication Page: https://www.backyardchickens.com/web/viewblog.php?id=19926-mud-eradication-project
and Pat's Fixing a Muddy Pen page: https://www.backyardchickens.com/web/viewblog.php?id=1642-fix-a-muddy-run
Both have lots of info. Mine also has pix. I would NOT use gravel on the top, as in addition to being hard on their feet it's also very hard to clean. I.e., you can hose the poop into it, but you can't separate poop from gravel to remove it. You CAN just pick it out of sand (I use a plastic horse pitchfork w/ hardware cloth zip-tied on to keep the poop from going through.
Sand over gravel is ideal. I used levelling sand.
and Pat's Fixing a Muddy Pen page: https://www.backyardchickens.com/web/viewblog.php?id=1642-fix-a-muddy-run
Both have lots of info. Mine also has pix. I would NOT use gravel on the top, as in addition to being hard on their feet it's also very hard to clean. I.e., you can hose the poop into it, but you can't separate poop from gravel to remove it. You CAN just pick it out of sand (I use a plastic horse pitchfork w/ hardware cloth zip-tied on to keep the poop from going through.
Sand over gravel is ideal. I used levelling sand.