Me and my brother spent the last two days using up all his materials to build up Spectacle Island (which I guess is now the worst location for a settlement on survival without fast travel).
We built a fancy 3-floor apartment for his favourite companions, plus a large 4-floor 'mansion' on the hill (with inner atrium) for himself.
It also has custom robot butlers and workbots to care for the land and residents.
We're just waiting on his levelling up to be able to make a bar for evening activities.
IMO, the most frustrating thing was wiring the place. I think they made the range on power conduits and pylons larger in an update (?), to help with wirelessly powering lights, and as a result we couldn't get seperate circuits on the different floors.
We wanted to have a switch to turn on lighting on the 3 lower floors, and a seperate one on the penthouse to light only that floor. But no matter what we couldn't stop the penthouse from overlapping with 2 floors below, so having top lights on meant some lower ones were on too.