Here are some ideas for the game:
Brick house:
A bit bigger then a timber house, but still smaller then a stone mansion.
Cost: 600 bricks.
Dig water:
Like that when you dig up around the 100-200 soil, the tile turns into a tile of water.
Bridge:
Costs: 40 boards, 4 blocks.
Has to be build on 2 tiles of ground, 8 tiles of water, and on the other side again 2 tiles of ground.
The 2 tiles of ground are horizontal, the 8 tiles of water are 4 vertically, 2 horizontally.
Needs a key to be opened. Can be opened from a little distance.