An aesthetic suggestion, and probably something along the color of dyes for buildings, etc.
wall covering materials:
-paneling in various textures already in the game (allowing to apply, for example, sandstone to one section of stonebrick wall - wall maintains stonebrick durability, but on the one face, it looks like sandstone, and on the other, like stonebrick). Implimenting this would allow the default to be the same on both sides, with the option of adding paneling to one side or the other to customize the interior/exterior) Damaging and/or decay of the panels would reveal the true material under it.
floor covering materials:
-carpet (square by square)
-ceramic tile floor - let us create our own mosaics with different colors/patterns
-larger windows, with the option of casements and shutters (like doors filling doorways).
-sloped roof/rooftop junctions (a junction where higher and lower roofs meet)
Snap to options for placeables:
-cupboards, chests, beds, etc to snap to/line up with walls, eachother, etc - At curser, push button to snap to eligible surface. push button again to snap to a DIFFERENT eligible surface. Cycle through eligible snap surfaces, including free placement (no snap). shift-button to back up one snap surface.