Brainstorm a list of elements, themes and features you want your can sculptures to include. This list can highlight contest requirements or things like an environmental theme, appropriate if you are designing the sculpture as part of a recycleable-items art contest, or motion, if you are leaning toward designing a series of kinetic sculptures that feature soda cans dangling from wires.
Sketch a variety of possible sculpture configurations, experimenting with materials and the orientations of the cans, such as upright, sideways, cut in half, cut apart and turned inside out. Keep the themes and desirable elements you listed previously in mind as you sketch. Consider how different materials could contrast with or otherwise enhance the cans in your sculpture -- a tree branch plucked from the forest floor, for example, would form a stark contrast with the sleek, mechanically shaped surface of a soda can.
Finalize the designs of the sculptures by making new, precise drawings of each one. With the final designs complete, you can determine how many cans you will need to complete your sculpture and begin to gather them.