+1 on building a coop on a platform....
I recently built an enclosure for my ducks that is on a platform and it works great. Having the house raised by 3' really helps with cleaning it out, harvesting eggs and adding another element of predator proofing against egg eating snakes. I designed mine so that the coop has a front door for the ducks (with a ramp) on the inside of the yard and two access doors (for me) on the outside of the coop. That way I can clean and harvest eggs without disturbing the ducks unnecessarily.
I
posted a video of my yard and coop here if you're interested.
Building a coop was pretty easy and you can get all the materials you need from your general big box store (HD/Lowes). It's also much cheaper and you get a much better product than anything you could purchase for the same amount of money.
Also, I filled my yard with sand. It is so much easier to clean a duck yard with sand then dirt/straw. Also, sand is easy on their feet and provides them a continual source of grit for their digestion (make sure you use construction sand, not sandbox/morter sand).
smithmal