To start off, I'll re-post the pictures from the pictures thread of the epic wall I built on 'Island' map, which won the game for both sides (I rebuilt on-top of the wall for the opposite team when i switched sides).
So game started on Island. I was Green, decided to spring into the middle of the map, made a small wall, then slowly expanded it to make a giant wall across the island. 4 blocks high and 4 thick at the bottom, all with bright green blocks. We used it to dominate the enemy for half an hour. Blues could barely get out of their spawn. I got a bit bored, switched to Blue and decided to hijack my wall and built a bigger, better wall on top of it. Now 5 bricks high, the game swung completely in Blues favour and now Green could barely leave their spawn. I like to think I was the most influential person on the teams, building both walls single-handedly. These are the results:
From on top:
From our side: (note the destruction caused on the ground from when it was a green wall)