Example instance based shipping method

class-wc-shipping-test-method.php

<?php
/**
 * Example of a custom WC_Shipping_Method class.
 */

if ( ! defined( 'ABSPATH' ) ) {
	exit;
}

/**
 * Class WC_Shipping_Test_Method.
 */
class WC_Shipping_Test_Method extends WC_Shipping_Method {

	/**
	 * Constructor. The instance ID is passed to this.
	 */
	public function __construct( $instance_id = 0 ) {
		$this->id                    = 'test_method';
		$this->instance_id           = absint( $instance_id );
		$this->method_title          = __( 'Test Method', 'textdomain' );
		$this->method_description    = __( 'Some shipping method.', 'textdomain' );
		// Apply this fee to all instances, on top of the cost. Can be a percentage.
		$this->fee                   = '0';
		// Set a minimum value for the fee; only useful with percentage based fees.
		$this->minimum_fee           = '0'; 
		$this->enabled               = $this->get_option( 'enabled' );
		$this->title                 = $this->get_option( 'title' );
		$this->supports              = array(
			'shipping-zones',
			'instance-settings',
			'instance-settings-modal'
		);
	    $this->instance_form_fields = array(
        		'enabled' => array(
        			'title' 		=> __( 'Enable/Disable', 'textdomain' ),
        			'type' 			=> 'checkbox',
        			'label' 		=> __( 'Enable this shipping method', 'textdomain' ),
        			'default' 		=> 'yes',
        		),
        		'title'   => array(
        			'title' 		=> __( 'Method Title', 'textdomain' ),
        			'type' 			=> 'text',
        			'description' 	=> __( 'This controls the title the customer sees during checkout.', 'textdomain' ),
        			'default'		=> __( 'Test Method', 'textdomain' ),
        			'desc_tip'		=> true
				),
				'cost'    => array(
					'title'             => __( 'Cost', 'textdomain' ),
					'type'              => 'text',
					'placeholder'       => '',
					'description'       => __( 'This controls the cost that is applied for this shipping method at checkout.', 'textdomain' ),
					'default'           => '100.00',
					'desc_tip'          => true,
					'sanitize_callback' => 'wc_format_decimal',
				),
		);

		add_action( 'woocommerce_update_options_shipping_' . $this->id, array( $this, 'process_admin_options' ) );
	}

	/**
	 * Calculate shipping for this method.
	 *
	 * @param array $package (default: array())
	 */
	public function calculate_shipping( $package = array() ) {
		// In this example, we're applying a single cost for the method,
		// but if you are using `per_item` tax caculation, you will need
		// to multiply the cost by the number of items in $package and
		// pass that figure in as the total instead.
		$total = wc_format_decimal( $this->get_option( 'cost' ) );

		$this->add_rate(
			array(
				'id'       => $this->id . ':' . $this->instance_id,
				'label'    => $this->title,
				'cost'     => $total + $this->get_fee( $this->fee, $total ),
				'calc_tax' => 'per_order', // Or `per_item` to calculate for each item.
			)
		);
	}
}

init.php

<?php
/**
 * Load our test method class when WC initialises shipping.
 *
 * @return void
 */
function init_wc_shipping_test_method() {
	if ( ! class_exists( 'WC_Shipping_Test_Method' ) ) {
		// Alter this accordingly to correctly include the class
		include 'class-wc-shipping-test-method.php';
	}
}
add_action( 'woocommerce_shipping_init', 'init_wc_shipping_test_method' );

/**
 * Add our test method to the list of available methods.
 *
 * @param array $methods Methods as method_id => class name.
 * @return void
 */
function add_wc_shipping_test_method( $methods ) {
    $methods['test_method'] = 'WC_Shipping_Test_Method'; 
    return $methods;
}
add_filter( 'woocommerce_shipping_methods', 'add_wc_shipping_test_method' );