Answer any questions at this point, and then announce that the representatives will return to the groups, and once they return, the facilitators will not answer any questions.
[The facilitators should not answer any questions so that the groups are forced to figure out how they want to build their tower on their own. If the groups figure out decide they need want to collaborate, the facilitators should neither encourage or discourage them (this will come up in the debrief).]
Announce that they have ~20 min to build, and let the building begin.