Welcome to OpenStreetMap.

The building tag should only be applied to the outlines of actual buildings, not the entire parcel of land.
https://wiki.openstreetmap.org/wiki/Key:building

The layer=-1 tag tells routers and renderers that features are at different levels.
https://wiki.openstreetmap.org/wiki/Key:layer

The historic=manor tag is probably better applied to the building itself (in this case, the Grade I listed Fairlawne), not the grounds.
https://wiki.openstreetmap.org/wiki/Tag:historic%3Dmanor

As Fiarlawne is presumably still a private residence, rather than a building operated by National Trust, English Heritage, etc., the original tagging of the surrounding area as landuse=residential was probably correct.

The formal gardens within the estate could be added as leisure=garden + access=private if you wanted more detail than just a pale grey area.
https://wiki.openstreetmap.org/wiki/Tag:leisure%3Dgarden

If you would like any help with this, please feel free to ask.