custom post type with role Vendor

First you have to passed two additional arguments into the register_post_type() function.

1. capability_type
2. map_meta_cap

Then, You can add capability using add_cap(); function.

register_post_type( 'acme_product',
    array(
      'labels' => array(
        'name' => __( 'Products' ),
        'singular_name' => __( 'Product' )
      ),
      'public' => true,
      'has_archive' => true,
      'capability_type'  => array('acme_product','acme_products'),
      'map_meta_cap'        => true,
    )
  );

    add_action('admin_init','vendor_role_caps');

    function vendor_role_caps() {

      $role = get_role('vendor_user');
      $role->add_cap( 'read' );
      $role->add_cap( 'read_acme_product');
      $role->add_cap( 'read_private_acme_products' );
      $role->add_cap( 'edit_acme_product' );
      $role->add_cap( 'edit_acme_products' );
      $role->add_cap( 'edit_others_acme_products' );
      $role->add_cap( 'edit_published_acme_products' );
      $role->add_cap( 'publish_acme_products' );
      $role->add_cap( 'delete_others_acme_products' );
      $role->add_cap( 'delete_private_acme_products' );
      $role->add_cap( 'delete_published_acme_products' );

 }