Just a few ides that have been occurring to me lately. The big one I think is the ability to make buildings translucent so you can build behind them. the other thing that would be cool would be bridges, low and high, make the low weaker so if they block a river you can break them but high bridges cost more material but allow boats and rafts under.
i would also like a way to make some sort of area defense obe ject a defense tower of some sort.
anyway i'll add more ideas as my they occur to me,