Well, here it is. My first Android app:
https://play.google.com/store/apps/details?id=com.disksize
Disk Size
Just a small app that shows you what files on your sd card are present, and the size of the files. This sorted from large to small.
Only two options for now. Top 10, or All files.
The app is developed as a learning project, but when you are learning, you might as well make something useful. So improvements will followa when learning new skills for the Android platform!