Conceiving a diorama is an adventure in scale and spatial relationships. Choose a container, then put yourself in the shoes of one of its future inhabitants.
Tools and Materials
Ham can (tin)
Styrofoam (an old cooler)
Bump chenille stems (pipe cleaners)
White glue
White paint
Borax
Figurines
Plastic wrap
White rubber band
Ski Slope Diorama How-To
1. To make the snowy scene, trace a well-washed ham can onto a piece of 1/2-inch-thick Styrofoam (an old cooler works well) five times. A grown-up should use a kitchen knife to cut slope shapes: The background layer should be full size; cut increasingly lower slopes from the other layers.
2. Glue in place. Cut bump chenille stems (fancy pipe cleaners) to make trees, trimming bristles off of bottom 1/4 inch of each for a trunk. To dust trees with snow, brush on white glue and sprinkle with borax, or spatter on white paint.
3. Poke trees into foam. Glue figurines, from a model-train store, into position. Stretch plastic wrap over the container, and secure with a white rubber band.
4. Using a toothbrush, spatter the plastic wrap with white paint for snow.

the edges of ham cans can be sharp
Quackyduck is absolutely correct ... Borax IS toxic. Martha's people should do better research on the components used in kids' projects.
Thank you for this great idea. My kids will love it.
Borax is toxic, so why is this a kids' craft?