There are many different kinds of tile. Not all tile needs to be sealed to be impervious to water. Ceramic tile like the kind used in bathrooms and kitchens is one obvious example. And I would imagine that installing tile as a coop floor would be done the same way you install tile elsewhere: you'd spread a bed of mortar, set the tiles, and then follow up with grout. You would need to seal the grout unless it was that special kind that doesn't need sealing.
We have a tile floor in our indoor birdroom, and it works great. It was there when we bought the house 25 years ago, though. I'm pretty sure I wouldn't have put it in especially for the birds.
Personally, I would think that installing a tile floor in a chicken coop would be more work than it's worth. There are so many other, easier options that work perfectly well. I just painted the plywood floors in our coops.
Now, if you had some left over tiles that you were just itching to use, and they were suitable for use as wall tiles, how about tiling a "backsplash" behind the roost?