I have a localhost Drupal 7.x installation on my system. I have just explored with UI and created a custom Content type which defines a form with radio boxes. (Home --> Structure --> Content types --> Add Content Type, and so on.)
I am assuming these custom content types will be stored in local directories of Drupal core. I am not able to figure out where exactly these stay. I am curious to make changes to that file and see if there is any reflection, though I am not sure if it works that way.
Content types are data structure under Drupal so those are not stored in files but in Database.
If you add a field type file as part of a content type you can define where those files will be placed into the field type configuration