Daily Calender for Users

I have an idea in mind to create a WP site that allows users to keep track of info on a daily basis. An example might be a weight loss tracking site, though that’s not what im working on. The idea is the same. I need users to be able to save this info daily, and create a pdf of any given day or month and view archives on a calendar. Any thoughts on how to accomplish something like this? I have ideas, just need some other thoughts.

Would I use a form? A post with custom fields? A custom post type? A form that creates a post or custom post? I like the last idea.

Thanks for reading.

[No bumping, thank you.]