Hi, it's a really good question.

If it's currently in use then landuse=animal_keeping https://wiki.openstreetmap.org/wiki/Tag:landuse%3Danimal_keeping

and then a barrier/fence around it.

If it's for ruins, then add a ruins tag to it. https://wiki.openstreetmap.org/wiki/Key:ruins

Let me know if you have any more questions.