I think you definitely need to consider the following factors: Needs analysis, design, resources, implementation and evaluation. I have put some thoughts on this together in a paper - see my profile to read it.
Are you planning to build a research instrument? Run a pilot study? Could you add some specifics, and I could provide some guidance. If you are planning to build, rather than use a third party, you need at least a well-thought idea (an app usually has a specific job to do, to serve a specific audience), resources to develop that idea (user experience designer, content producer, programmer, usability tester, etc.), and a clearly identified audience. That process probably would involve creating a team of collaborators (unless you are incredibly multi-talented), and it probably will need some seed money.