Sure, you can make your own. You need to decide if you want a ruffled skirt or a tailored (non ruffled, just one or two pleats). If you are limited on the amount of fabric, the tailored one will take much less. You can also just pin the skirt to the box spring, or use an older sheet or ugly fabric to make the decking, as it will not show.
If you do a google search, there are lots and lots of instructions.
Here's an example of a tailored version:
http://www.mybackyardeden.com/2010/0...bed-skirt.html
here's a ruffled one:
http://thedomesticdiva.wordpress.com...a-dust-ruffle/