If you have been using apps regularly, you can build your own app easily. This is because most of the apps out there are not perfect. Just take an objective look at some of the apps you have used in recent times. Now, get a piece of paper and a pen and list the pros and cons of these apps. If you have noticed some obvious shortcomings in the apps you are using, you can work on these shortcomings and come up with an improved version when you build your own app.
If you do not want to go this route, you can simply create your own app from scratch. Just think about a program that will help many people in your area and create an app based on your observations. In most cases, apps are created to solve problems or to meet a need. Create your own app and you will help the society.