In many traditions of Wicca and Paganism, the four classical elements of Earth, Air, Fire and Water are considered significant. To make an altar cloth that represents all four of them, you'll need to select four different kinds of fabric -- one for each element, and get about 1/4 to 1/2 yard of each, depending on how big you want to make your altar cloth.
When selecting your fabrics, make sure each material is of a similar weight -- you don't want to try stitching together satin, a heavy brocade, and tulle all in the same project. Quilter's cotton is a great fabric to use, and it's reasonably priced -- usually under $3 per yard. You may wish to pick a material with a design -- I used a green one with leaves for Earth, blue with clouds for Air, etc. -- or you might just want to go with colors that symbolize the elements in your tradition.