Here's the set up we have so far for our runners:
The whole thing is about 40' long by 15' wide and maybe 6' tall (we recently got taller fence posts so that we could raise the overhead netting enough to be able to walk around upright inside the pen. It's an ongoing project by all means; there are a lot of things we would like to make nicer-looking and sturdier, and that pile of blocks and black plastic in the back corner is a bigger pond that we still need to get set up, but so far it's kept our little flock safe and happy.
And of course, they're constantly working on excavating their own little river with the overflow from the pond. It doesn't look like much when the puddles are filled, but it's a series of fairly deep holes that stretches across the width of the pen.
The grass comes and goes, of course, with all the stomping and drilling. I've taken to using a collapsible steel ex pen to block off portions of the pen for a couple weeks at a time, to give the groundcover a chance to grow back. It's a pain, but it keeps the whole pen looking and smelling much nicer!