Yeah I was deciding whether to include the outdoor seating area. It's a raised deck attached to the building and was already traced by another mapper but untagged, so I decided to include it.

The Dixon building will be simpler, so I'll have a crack at it sometime soon.

I gave your suggestion a go on a cafe I visited recently that already had a hodgepodge of buildings and parts and nodes: changeset/178000466
I used a building for the outside perimeter then parts for each section. Let me know if this is what you were thinking and I can do the same for the Thomas Dixon Centre.

Yes, I made sure there were no intersecting rings or touching inner rings. I can't find anything about touching outer rings on the following pages:
osm.wiki/Relation:multipolygon
osm.wiki/Relation:multipolygon/Algorithm
osm.wiki/Talk:Relation:multipolygon
osm.wiki/Proposal:Relation:multipolygon/validity
https://www.ogc.org/standards/sfs

Valid multipolygons appears to be a decades old debate with no clear consensus, anyway.

Please map the building according to best practice and I will study it and follow along accordingly in my future mapping.

Hi, thanks for the suggestion. I've read through the OSM wiki article on 'relation:multipolygon' twice to learn more about multiplygons and haven't found anywhere suggesting not to use shared segments.

It does mention in the subheading 'Mapping style, best practice' that "sharing way segments between multipolygons (method B) offers a representational efficiency by avoiding redundant representations of overlapping ways."

Is there something I'm misunderstanding? Would love to learn more so I don't make bad contributions!