I know these couldn’t be added until AFTER day 1, but I thought I’d suggest it now.
I would like to suggest walls and doorframes for all tiers of construction designed only for interior use in buildings. These would be identical to the same tier wall/doorframe, but would visually look like the inner walls on both sides. These would be for separating a building or floor into two or more rooms. It’s purely aesthetic, but half the reason I play this game is “pretty pretty base building”.