Once you have a template for the correct size of panel - the shape needs to be traced onto carboard sheets - cut out and assembled into a hollow sphere.  The accompanying pictures illustrate how I do it.  Note the orientation of the cardboard.

This sphere was for the "snowball outfit" and was subsequently covered with white quilt batting Cardboard costumes. On some costumesI install LED lighting by using a battery pack and christmas tree lights. LED lights run off almost any power source and consume almost no battery life.

Please note:

This series of photgraphs show how the cardboard panels are cut out and assembled into a hollow sphere. Since these photos were taken - I now use 16 panels to make a ball, and I tape over the outer seams with 2 inch strips of kraft paper glued to the cardboard with carpenter's white glue.  If the outer seams have crinkles  - and they always do - I iron them flat with a hot iron after presssing them in place. Use of the hot iron smooths out the tape and sets the glue quickly.  It yields an aaalmost invisible joint which is also quite strong.