With iwiw60 110%...sand gets really gross really fast if it is not coarse grain and covered. I recently renovated my coop and took down my sand filled run...boy that was the most disgusting process that I ever partook in. If you have sand, I would highly suggest that you cover it, and pretty much treat it like cat litter. Also, if you can find very coarse grain sand, buy it. Try and put your run on uneven ground so that water will drain outward and not pool in the sand. Try and keep the depth to no more than six inches. Covering old and filthy sand with new sand is a temporary fix, and the day of reckoning will come when you have to clean it out!
These are just my experiences. I know there are a lot of people on this forum who have used successfully, but I am not one of them. No new run is simply earth that has been covered in a mixture of hay and foliage. I will use tree leaves in the fall when they are bountiful and bag a few more to use throughout winter. This will help me save a little on hay over winter (even though it is something like 5 bucks a bale, and one bale lasts me three cleanings (so roughly lasts 1 and 1/2 months.