I know this has been suggested in another form already but this is purely targeted towards building blocks.
Something that would really help with large scale projects is snapping for building blocks.
A way I was thinking is having spheres on the places the piece could possibly snap to and having these be dynamic according to the piece being placed.
Ex: Snapping a full wall to a full wall
Ex: Snapping a Quarter piece to a full wall
There is probably a much better way to do this but for Quarter pieces and such it would be really nice to have it be flexible with how it snaps to the piece.