Thanks for the message. To address each point:
1. I've found a few that didn't quite match on the north face of the building - fixed now. All nodes link to the outer edge of the building where they should; nodes that are away from the edge of the building are deliberately so for the facades (see below) and for the angled roof sections which meet in the middle.
2. Thanks for that, I've removed the construction tags on the building - the surrounding area is still under construction, so is correct.
3. Yes, this is representative of what is on the ground (while using the newest imagery as a reference).
4. Roof sections are tagged with building:material, not roof:material, because their outer walls are concrete. However it's probably more elegant to place the building:material in the main building, so I've done so and removed from each of the building:parts.
5. This facade could potentially be a barrier=wall with material=glass instead of a polygon I suppose - not sure it would render well in 3D though, and the East wall would still need to have the current setup anyway (as the angled roof shape is also part of the polygon). There are pros and cons to either approach, not least that technically it should be a "part" of the building construction, rather than a separately mapped line. But I'm open to suggestions.