Rails 3: User Created custom forms?

I am trying to wrap my head around how to allow a user to create custom forms with all the field types. If there is a gem that would be great, but I cannot seem to find one anywhere.

So I have a DB setup like this which:

  t.integer :form_id
  t.string :name
  t.string :hint
  t.integer :position
  t.string :field_type
  t.boolean :required
  t.integer :size
  t.boolean :multiple
  t.text :values
  t.timestamps

And this is pretty much where I am. I cant think of how to iterate thru the field_type and return the values, as well as associate them with forms actually being filled out.

Thanks