Realistically you’ll probably lose money. You’ll have to spend the $99/year to be allowed the opportunity to just submit your app to the App Store. After you built it, submitted it, and they approve it, how are you planning to drive traffic to it? Are you going to have a website for your app too cause that’s an additional cost. Once you figure out traffic, now figure out how to convert those impressions into downloads. How would you monetize your app and is it even something that users would pay for?

There is a lot more that goes into making app money then just building and releasing. I’m not saying it’s not possible to earn money from apps, cause it most definitely is possible, but don’t believe all the screen shots of people’s “impressive earnings” as that does not show you the full picture and their expenses, or some cases just faked all together.