There are some iOS FlatUI libraries. I collect them.
These designs may help you to think your app's design.
23 Flat Design iPhone Apps - DesignM.ag
http://designm.ag/design/23-flat-design-iphone-apps/
Dribbbleに投稿されたフラットなiOSのデザイン - Newthy
http://newthy.systemagic.jp/news/19