YP must replicate a model made by a leader in the fastest time.
Each group (recommended 3-5) gets an identical set of Lego, with a leader also getting an identical set. A leader places an open-topped box in the middle of the room and constructs a model out of some of the pieces available. Groups are allowed one person at a time to come up to the box and look at the model without touching it; the first group to construct the same model and bring it to the leader wins.
Models with 4-5 pieces are good to start out with. You can then add more pieces to the models each round to make it progressively harder.
Optional extras to increase difficulty:
-Wider variety of Lego pieces
-Once a YP has looked at the model, they are not allowed to touch any pieces of Lego (and therefore must explain to other team members how to construct it)
-Randomly give out handicaps to team members, including: can't touch, can't speak, can't walk.