Originally it was going to be 5 foot high, but I changed it to 6.5 feet at the last minute so I didn't have to stoop through a tiny door! The floor is half sand, half slate (I liked the slate as itd be nich easier to keep clean, but I was unsure if its be too much for their feet so I gave them a bit of both. They seem to be happy running around on it though).
PS please excuse the state of the garden! I finished hours before picking up the ducks and hadn't had chance to tidy up!
The last thing in considering is putting a corrugated pvc roof on it at some point