I can see where that site can/may/is going to create problems. The site as much as it wants to be well intentioned, is going to probably end up to be one of people taking apart other's costuming creations more than it will be of a learning how-to, as I suspect the person who created the site is hoping for.
Many years ago the Costumer's Guild (created here in S. Calif.) was started by people I know who were heavily into costuming. There are three catagories, Novice, Journeyman, and Master. I have the whole book and how to judge such competitions. It took me many years to become a Master costumer.
Not a site I choose to participate in.