I make crib quilts, and in the past have crocheted crib blankeys. The size should be about 42" by 34", give or take a couple of inches on either end.
I have a thought about the ribbon: you might want to rethink that, as the mom has to launder the blanket thousands of times over the years, often to remove vomit and other bodily productions. Ribbon may not last...
You might consider just doing a single or double stitch, or a double double stitch, or even a small shell stitch, all around the border.
There are many free crochet patterns on the internet if you want to Google. I don't know if these will help but they're a start:
http://www.crochetpatterncentral.com...by_afghans.php
http://www.craftown.com/baby/pat9.htm