Add custom schema to post

I’ve used a custom field and added the data above which works well but isn’t user friendly.

Use Custom Post Types and add Meta Boxes to make it user friendly.

Here’s a basic example of adding a custom post type:

function create_post_type() {
  register_post_type( 'car',
    array(
      'labels' => array(
        'name' => __( 'Cars' ),
        'singular_name' => __( 'Car' )
      ),
      'public' => true,
      'has_archive' => true,
    )
  );
}
add_action( 'init', 'create_post_type' );

Suggestion
You can also include Custom Taxonomies for fields like category, price_type, make, model, advert_type, etc.