You could use a [lifecycle prefix](//wiki.openstreetmap.org/wiki/Lifecycle_prefix) to describe the former building tag: `disused:building=greenhouse` (plus `building=warehouse`). I guess it still looks quite like a greenhouse, so this information may be useful (e.g. as navigation aid, or for (3D) rendering). I even would tend to keep the `building=greenhouse` tag, because it still is ("on the ground") a greenhouse – it is just not used as greenhouse. But the The building tag describes not the use of a building, but the building itself. The landuse tags should be on the land which is used for some purpose… usually bigger than the building.

You could use a [lifecycle prefix](//wiki.openstreetmap.org/wiki/Lifecycle_prefix) to describe the former building tag: `disused:building=greenhouse` (plus `building=warehouse`). I guess it still looks quite like a greenhouse, so this information may be useful (e.g. as navigation aid, or for (3D) rendering). I even would tend to keep the `building=greenhouse` tag, because it still is ("on the ground") a greenhouse – it is just not use used as greenhouse. But the building tag describes not the use of a building, but the building itself. The landuse tags should be on the land which is used for some purpose… usually bigger than the building.

You could use a [lifecycle prefix](//wiki.openstreetmap.org/wiki/Lifecycle_prefix) to describe the former building tag: `disused:building=greenhouse` (plus `building=warehouse`). I guess it still looks quite like a greenhouse, so this information may be useful (e.g. as navigation aid, or for (3D) rendering). I even would tend to keep the `building=greenhouse` tag, because it still is ("on the ground") a greenhouse – it is just not use as greenhouse. But the building tag describes not the use of a building, but the building itself. The landuse tags should be on the land which is used for some purpose… usually bigger than the building.