title: CodeIgniter classifieds I need DB sketch
body: <p>I can't image how to create classifieds structure.
  Example I have page for cars ads, and there can be fields year, price, and more.
  And I have page for mobile phones where can be fields price, color, display size and so on. For another page can be another fields and I need add them dinamicly, it can bee select field, text input, or maybe checkbox.</p>
  
  <p>So how I can add new fields for filtering ads, where to keep form validation rules?</p>
  
  <p>Can someone please give me a sketch of db that can me explain all this process?</p>