This happened to me a few times recently whilst building some absolute monster size houses. I literally hit the save button every 20 mins now, just incase lol
I'd like to see custom stairs, conservatories (inc glass roof). I agree with the comment above re - foundations. Having different heights would be great. I'd also like to see different height walls per floor level, symmetry in builds is good, but it would be so cool to mix it up a bit more :)