I personally like masonry sand.No bugs or worms like it and it makes the pen look so clean,plus it has very good drainage if it gets wet.
In N.H.,Tony.
Then I agree with Tony, masonary sand. It will drain well and will be easy for you to rake up the droppings. If you have a lot of clay in your soil where drainage is an issue, you may want to dig down, add some pea gravel a layer of landscape cloth, then the sand.
Take some pictures and share the progression of your project.
Good luck!
Bosque.
I use some homemade mulch In my Edwards pens from hardwoods ground up using my 3 point wood chipper.. Bugs don't seem to like hardwood chip, Use mostly oaks Branches..