I've used sand in all instances--on concrete, wood, and with dirt as a base. For my runs I always used sand that was placed directly on the existing soil base. No digging out; no disturbing the soil unless it needed some compaction. Then I rolled it.
The key is, however, what the humidity levels are in your area. Now I live in the deserts of Texas at 3500 foot altitude. My sand floors dry out quickly after a rain (we get 3 to 9 inches a year--3 has been our average totals for the past few years), as do the droppings. Sand is ideal for my purposes as my acre is almost pure sand. Look at my avatar photo--that's all sand. If you live in Florida or the humid regions of our country--the deep south or the east--you might NOT want to use sand. Some of my pigeon pens have expanded metal floors over sand. So my chicken pens all have floors of sand.