I had twin pygmies born during a freak april snowstorm last year and needed the coats in a hurry.
I had the coats already cut out. I used several layers of fleece and sewed the fronts shut. But I still needed a band to keep them on.
I used soft fleece horse leg wraps that I had sitting around here. They already had the velcro on the end and I just cut it to the length I needed. I didn't sew them to the blankets, just wrapped it around the belly over the coat and it worked great. It would only take a minute to sew them onto the blanket, but the babies grow so fast that I left them seperate so I could use them with other blankets.
For people that prefer a pattern their is a dog coat pattern that works well for goats too.