One Brick Short is the sixth mission in WorldBuilder.
Move the camera to the east side of the river, then build a Dirtbuggy with the pieces scattered about. Pick up the plans for the Tugboat, and build it on the water. Pick up the lone yellow brick in the middle of the river and place it with the stack of bricks floating on the water. Build a Dirtbuggy on the land and drive it to the goal.
Pick up the plans for the Buggy, then take apart the Dirtbuggy on the spot where the stack of red bricks is located. Build a Buggy and drive it near the river, then take it apart; use the Tugboat to carry the pieces over to the other side, then re-build the Buggy and drive it to the goal.