I thought I would see if I could help. I own a moby wrap that I purchased off of craigslist. Got it for $20. I really enjoyed it until baby got bigger and it took more time to put on.Anyways there were a couple of sites that I found by typing free baby sling pattern into my yahoo search. Here are a couple. They look like they would be easy to follow. Hopefully this will help you.
http://www.mykarmababy.com/pages/BabySlingPattern.php
http://www.handmade-adelaide-baby.co...pattern-2.html