WP Plugin permissions – create new files

I can think here of two possibillites.

  1. Use the wp-content/uploads maybe for your text-file because the file
    permission restriction are more or less bypassed in this directory.
  2. Put all stuff to wp_options and write a page Template imitating the text-file like page_text.php

    /* Template Name: Text-Template */ 
    echo get_option('ads', false);
    

Create a page and asign the Text-Template and you have a virtual text-file