Field clone example, doesn't work with actual DS fields that aren't on the entity.

FieldCloneBase.php

<?php

/**
 * @file
 * DS field clone base.
 */

namespace Drupal\mymodule;

use Drupal\ds\Plugin\DsField\DsFieldBase;
use Drupal\Core\Entity\EntityTypeManagerInterface;
use Symfony\Component\DependencyInjection\ContainerInterface;


/**
 * Abstract class to serve as a base for field clones.
 */
abstract class FieldCloneBase extends DsFieldBase {
  /**
   * Entity manager.
   *
   * @var EntityTypeManagerInterface
   */
  protected $entityTypeManager;

  /**
   * Field to clone.
   *
   * @var (string)
   */
  protected $field;

  /**
   * {@inheritdoc}
   */
  public function __construct(array $configuration, $plugin_id, $plugin_definition, EntityTypeManagerInterface $entity_type_manager) {
    parent::__construct($configuration, $plugin_id, $plugin_definition);
    $this->entityTypeManager = $entity_type_manager;
    $this->field = FALSE;
  }

  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
    return new static(
      $configuration,
      $plugin_id,
      $plugin_definition,
      $container->get('entity.manager')
    );
  }

  /**
   * {@inheritdoc}
   */
  public function build() {
    $room = $this->entity();
    $config = $this->getConfiguration();

    $viewBuilder = $this->entityTypeManager->getViewBuilder('node');
    $output = FALSE;

    if ($this->field !== FALSE) {
      $field = $room->{$this->field};

      $output = $viewBuilder->viewField($field, $config['view_mode']);
    }

    return $output;
  }

}

SomeFieldClone.php

<?php

/**
 * @file
 * DS price field clone.
 */

namespace Drupal\mymodule\Plugin\DsField;

use Drupal\mymodule\FieldCloneBase;
use Drupal\Core\Entity\EntityTypeManagerInterface;

/**
 * Plugin that renders a clone of a field.
 *
 * @DsField(
 *   id = "mymodule_some_field_clone",
 *   title = @Translation("DS Field: Some field clone"),
 *   entity_type = "node",
 *   provider = "mymodule",
 *   ui_limit = { "room|*"}
 * )
 */
class SomeFieldClone extends FieldCloneBase {

  /**
   * {@inheritdoc}
   */
  public function __construct(array $configuration, $plugin_id, $plugin_definition, EntityTypeManagerInterface $entity_type_manager) {
    parent::__construct($configuration, $plugin_id, $plugin_definition, $entity_type_manager);
    $this->field = 'field_some_field';
  }

}