It would be really cool if we could build a tiny starter building out of clay, straw and branches. Of course such a hut might not be bear or boar proof.
A wider variety in general would be nice- I'd like to see stone, plaster, brick, and various forms of wood being used. Also nice would be some rotations.
I further propose that buildings should be in the same world-space as the rest, making windows trivial. Of course, this would require things like fading roofs, but that will need to be addressed anyway; see "I lost my cart behind the standing stoooones!"