I'm not a 3-d person either, but I will never forget a project from my
college 3-d class.
Actually this project has been done with cub scouts and science classes as
well as art classes. The objective is to construct a 3-d container that will
protect a raw egg from breaking when the container is dropped from a height.
Did this with cub scouts. They loved it but too many eggs made it because we
only dropped them from a step ladder.
In college we dropped them off a second story balcony and yes some of the
eggs made it.
There is a science lesson here, but you could just focus on the visual
aspects. Is the form important to the egg not breaking or is form a
decorative aspect. Maybe the containers need to resemble animals? Speaking
of animals, paper mache pinatas are fun to make.
Also have made Louise Nevelson scultptures from cardboard boxes and pieces.