How to start a iphone case business?

I'm 13 and I really need money. There aren't a lot of things i can do for money at the moment other than chores and that isn't making me alot. So I want to start a small business online just making Iphone 4/4s and 5 cases and selling them. I would have a tumblr or instagram for the cases/business. Where can i make/order some cases online to customize for my business? I'm looking for them to be as cheap as possible.

Work on the internet.imma working there for few years and making $xxx day