The following entry is not done yet. It will be edited throughout the days.
I would build a Bridge Puzzle, a car bridge that keeps randomly turning (like a 1x1xX) during random points during the bridge. When it turns, it kind of is like a speed bump, except it is literally do or die. When you cross while the bridge is rotated up, you will fall into water. It is a pretty fun bridge to cross, and you wouldn't really have to worry about bad drivers; they'll be dead after a few seconds. I would make this because:
1. Keeps away drunk driving *****s.
2. It would be huge, like no other puzzle.
3. It would be seen by all people, making cubing popular.
4. It's fun to cross a bridge that is a puzzle; your brain really gets going.
5. When you cross, you can brag that you have accomplished yet ANOTHER acheivement.
By the way, the solving part of this puzzle is not moving during the blocks being vertical. If you move during that point in time, it is considered unsolved.
I'll draw a picture soon.