Excellent initiative on wanting to get involve. However, I would suggest researching a project that is already on-going and contribute towards that.
If you start a new project on GitHub, SourceForge or BitBucket, it will be most likely have a team member of 1 (you). The problem is not that your project is not open sourced, but that you are the only one working on it.
If a job candidate tells me they are involve in an open source project, I would look at the project for some of the following characteristics.
- size of the code base, a large code base shows that you can handle a project will some complexity in functionality and implementation.
- size of the project team, it indicates that you can work in a team successfully with good communication skills with your team members. Also how you interact with their programming styles.
- code quality, the quality of your contribution has good comments, nicely structured, working on code from others
- time spent on project, shows that you have commitment with define start and end points.
Being a contributor does not necessary contributing to the code. You could contribute to up keeping of the documentation, or do some translation.
My point being is that everything that you do in this space is valuable to your resume, but do it with a team.