Hi TinTin, welcome to OSM editing, thank you for your contributions.
The `surface` tag is intended for the surface of highways (roads, tracks, paths). For a building, the tag you are looking for is `building:material`

Check the OSMWiki it is the reference for tags: https://wiki.openstreetmap.org/wiki/Key:building:material
            ---
            
            Published using OSMCha: https://osmcha.org/changesets/136208088
            