Good resources for outlining site/app construction?

All the narratives I encounter about non-techs learning to code stress the importance of learning by working on a product you care about. After a 2 week crash course in Rails and Ruby, I feel like it's time to dive into building my first webapp. I'm wondering if anyone knows any good resources that could help a first time developer like myself outline my project. Some kind of to-do list or outline or draft structure or roadmap? Any help appreciated!