There are several different types of deserts; hot and dry, semiarid, coastal and cold deserts. The criteria for a desert is an area that has less than 50 cm a year of rain. Once the particular desert is chosen, make a list of its vegetation and animals, and make note of how the terrain is laid out. Gather photos from the Internet or books from the library to help in the research.
Typically, a shoebox is used to build a diorama, but any box will work. Consider using a tall, thin box vertically or horizontally. Connect a few boxes together that tell a story. Show different events that happen in multiple boxes. For example one box can show the desert during the day, another can display a scene from the desert at night, and still another can show what happens to the desert during a flash flood.
A diorama is designed to show a three-dimensional scene. Draw or place an image on the back wall of the diorama, and continue adding layers from there. Create sand dunes by building up the floor of the diorama with clay. Spread a layer of glue over the top, then sprinkle a layer of sand. Use all the sides of the container. Hang clouds, or birds from the top of the container, tape plants and animals made from cardboard or clay, or ready-made animal figurines throughout the box. Working from the back to the front, the objects should get larger to give the impression of perspective.
Go beyond the correct life forms and tell a story with the placement and choice of objects. The scene can show predators and prey, or you can make the diorama come to life by bringing in multimedia effects. A hot desert can have the recorded sound of a sizzling fried egg playing in the background, or a desk lamp pointed directly over the display.