Cut strips to make up your skirt. To figure out how wide you want your strips to be decide how long you want the skirt and add 3 inches for your seam allowances, hem, and casing. Then divide by the number of stripes you want and cut your fabric to that size. Mine was a 3T and each strip of fabric was 3.5 inches wide by 44 inches (the width of my fabric bolt) long. So I needed just 7 inches of each fabric so 1/4 of a yard of each would have been more than enough. See this chart for some general measurements for different sizes.

Sew the stripes together to form a striped fabric. Finish the seams with a serger, zig zag, or overlock stitch on your sewing machine.

Then sew up the short side to form a tube.

Finish both edges and fold the bottom edge under 1/4 inch and stitch around to hem.

Fold the top edge under 1 inch and sew leaving a hole for your elastic.

Thread in your elastic and close up the hole in your casing.