mkdir -p packages/Webkul/CustomExpressShipping/src/{Carriers,Config,Providers}

<?php

return [
    'custom_express_shipping' => [
        'code'         => 'custom_express_shipping',
        'title'        => 'Express Delivery (1-2 Days)',
        'description'  => 'Premium express shipping with tracking',
        'active'       => true,
        'default_rate' => '19.99',
        'type'         => 'per_order',
        'class'        => 'Webkul\CustomExpressShipping\Carriers\CustomExpressShipping',
    ],
];

<?php

namespace Webkul\CustomExpressShipping\Carriers;

use Webkul\Shipping\Carriers\AbstractShipping;
use Webkul\Checkout\Models\CartShippingRate;
use Webkul\Checkout\Facades\Cart;

class CustomExpressShipping extends AbstractShipping
{
    /**
     * Shipping method code - must match carriers.php key.
     *
     * @var string
     */
    protected $code = 'custom_express_shipping';

    /**
     * Shipping method code.
     *
     * @var string
     */
    protected $method = 'custom_express_shipping_custom_express_shipping';

    /**
     * Calculate shipping rate for the current cart.
     *
     * @return \Webkul\Checkout\Models\CartShippingRate|false
     */
    public function calculate()
    {
        if (! $this->isAvailable()) {
            return false;
        }

        return $this->getRate();
    }

    /**
     * Get shipping rate.
     *
     * @return \Webkul\Checkout\Models\CartShippingRate
     */
    public function getRate(): CartShippingRate
    {
        $cart = Cart::getCart();

        $cartShippingRate = new CartShippingRate;

        $cartShippingRate->carrier = $this->getCode();
        $cartShippingRate->carrier_title = $this->getConfigData('title');
        $cartShippingRate->method = $this->getMethod();
        $cartShippingRate->method_title = $this->getConfigData('title');
        $cartShippingRate->method_description = $this->getConfigData('description');
        $cartShippingRate->price = 0;
        $cartShippingRate->base_price = 0;

        $baseRate = (float) $this->getConfigData('default_rate');

        if ($this->getConfigData('type') == 'per_unit') {
            foreach ($cart->items as $item) {
                if ($item->getTypeInstance()->isStockable()) {
                    $cartShippingRate->price += core()->convertPrice($baseRate) * $item->quantity;
                    $cartShippingRate->base_price += $baseRate * $item->quantity;
                }
            }
        } else {
            $cartShippingRate->price = core()->convertPrice($baseRate);
            $cartShippingRate->base_price = $baseRate;
        }

        return $cartShippingRate;
    }
}

<?php

return [
    [
        'key'    => 'sales.carriers.custom_express_shipping',
        'name'   => 'Custom Express Shipping',
        'info'   => 'Configure the Custom Express Shipping method settings.',
        'sort'   => 1,
        'fields' => [
            [
                'name'          => 'title',
                'title'         => 'Method Title',
                'type'          => 'text',
                'validation'    => 'required',
                'channel_based' => true,
                'locale_based'  => true,
            ],
            [
                'name'          => 'description',
                'title'         => 'Description',
                'type'          => 'textarea',
                'channel_based' => true,
                'locale_based'  => false,
            ],
            [
                'name'          => 'default_rate',
                'title'         => 'Base Rate',
                'type'          => 'text',
                'validation'    => 'required|numeric|min:0',
                'channel_based' => true,
                'locale_based'  => false,
            ],
            [
                'name'          => 'type',
                'title'         => 'Pricing Type',
                'type'          => 'select',
                'options'       => [
                    [
                        'title' => 'Per Order (Flat Rate)',
                        'value' => 'per_order',
                    ],
                    [
                        'title' => 'Per Item',
                        'value' => 'per_unit',
                    ],
                ],
                'channel_based' => true,
                'locale_based'  => false,
            ],
            [
                'name'          => 'active',
                'title'         => 'Enabled',
                'type'          => 'boolean',
                'validation'    => 'required',
                'channel_based' => true,
                'locale_based'  => false,
            ],
        ],
    ],
];

<?php

namespace Webkul\CustomExpressShipping\Providers;

use Illuminate\Support\ServiceProvider;

class CustomExpressShippingServiceProvider extends ServiceProvider
{
    /**
     * Register services.
     *
     * @return void
     */
    public function register(): void
    {
        $this->mergeConfigFrom(
            dirname(__DIR__) . '/Config/carriers.php',
            'carriers'
        );

        $this->mergeConfigFrom(
            dirname(__DIR__) . '/Config/system.php',
            'core'
        );
    }

    /**
     * Bootstrap services.
     *
     * @return void
     */
    public function boot(): void
    {
        //
    }
}

{
    "autoload": {
        "psr-4": {
            "Webkul\\CustomExpressShipping\\": "packages/Webkul/CustomExpressShipping/src"
        }
    }
}

composer dump-autoload

<?php

return [
    App\Providers\AppServiceProvider::class,

    // ... other providers ...

    Webkul\CustomExpressShipping\Providers\CustomExpressShippingServiceProvider::class,
];

php artisan optimize:clear

<?php

namespace Webkul\Shipping\Carriers;

use Webkul\Shipping\Exceptions\CarrierCodeException;

abstract class AbstractShipping
{
    /**
     * Shipping method carrier code.
     *
     * @var string
     */
    protected $code;

    /**
     * Shipping method code.
     *
     * @var string
     */
    protected $method;

    abstract public function calculate();

    /**
     * Checks if shipping method is available.
     *
     * @return array
     */
    public function isAvailable()
    {
        return $this->getConfigData('active');
    }

    /**
     * Returns shipping method carrier code.
     *
     * @return string
     */
    public function getCode()
    {
        if (empty($this->code)) {
            throw new CarrierCodeException('Carrier code should be initialized.');
        }

        return $this->code;
    }

    /**
     * Return shipping method code.
     *
     * @return string
     */
    public function getMethod()
    {
        if (empty($this->method)) {
            $code = $this->getCode();

            return $code . '_' . $code;
        }

        return $this->method;
    }

    /**
     * Returns shipping method title.
     *
     * @return array
     */
    public function getTitle()
    {
        return $this->getConfigData('title');
    }

    /**
     * Returns shipping method description.
     *
     * @return array
     */
    public function getDescription()
    {
        return $this->getConfigData('description');
    }

    /**
     * Retrieve information from shipping configuration.
     *
     * @param  string  $field
     * @return mixed
     */
    public function getConfigData($field)
    {
        return core()->getConfigData('sales.carriers.' . $this->getCode() . '.' . $field);
    }
}

<?php

namespace Webkul\Checkout\Models;

use Illuminate\Database\Eloquent\Model;
use Webkul\Checkout\Contracts\CartShippingRate as CartShippingRateContract;

class CartShippingRate extends Model implements CartShippingRateContract
{
    protected $fillable = [
        'carrier',
        'carrier_title',
        'method',
        'method_title',
        'method_description',
        'price',
        'base_price',
        'discount_amount',
        'base_discount_amount',
        'tax_percent',
        'tax_amount',
        'base_tax_amount',
        'price_incl_tax',
        'base_price_incl_tax',
        'applied_tax_rate',
    ];
}

public function calculate()
{
    if (! $this->isAvailable()) {
        return false;
    }

    $cartShippingRate = new CartShippingRate;
    $cartShippingRate->carrier = $this->getCode();
    $cartShippingRate->carrier_title = $this->getConfigData('title');
    $cartShippingRate->method = $this->getMethod();
    $cartShippingRate->method_title = $this->getConfigData('title');
    $cartShippingRate->method_description = $this->getConfigData('description');
    $cartShippingRate->price = 15.99;
    $cartShippingRate->base_price = 15.99;

    return $cartShippingRate;
}

public function calculate()
{
    if (! $this->isAvailable()) {
        return false;
    }

    $cart = Cart::getCart();
    $baseRate = 5.00;
    $perKg = 2.50;

    $price = $baseRate + ($cart->weight * $perKg);

    $cartShippingRate = new CartShippingRate;
    $cartShippingRate->carrier = $this->getCode();
    $cartShippingRate->carrier_title = $this->getConfigData('title');
    $cartShippingRate->method = $this->getMethod();
    $cartShippingRate->method_title = $this->getConfigData('title');
    $cartShippingRate->price = core()->convertPrice($price);
    $cartShippingRate->base_price = $price;

    return $cartShippingRate;
}

public function calculate()
{
    if (! $this->isAvailable()) {
        return false;
    }

    $cart = Cart::getCart();
    $threshold = (float) $this->getConfigData('free_shipping_threshold');
    $price = $cart->sub_total >= $threshold ? 0 : (float) $this->getConfigData('default_rate');

    $cartShippingRate = new CartShippingRate;
    $cartShippingRate->carrier = $this->getCode();
    $cartShippingRate->carrier_title = $this->getConfigData('title');
    $cartShippingRate->method = $this->getMethod();
    $cartShippingRate->method_title = $this->getConfigData('title');
    $cartShippingRate->price = core()->convertPrice($price);
    $cartShippingRate->base_price = $price;

    return $cartShippingRate;
}

class Shipping
{
    public function collectRates()
    {
        // Iterates through all carriers and calls calculate()
        // Returns grouped shipping methods with rates
    }

    public function getGroupedAllShippingRates()
    {
        // Returns rates grouped by carrier
    }

    public function getShippingMethods()
    {
        // Returns available shipping methods
    }
}

packages
└── Webkul
    └── CustomExpressShipping
        └── src
            ├── Carriers
            │   └── CustomExpressShipping.php         # Rate calculation logic
            ├── Config
            │   ├── carriers.php                     # Shipping method definition
            │   └── system.php                        # Admin configuration
            └── Providers
                └── CustomExpressShippingServiceProvider.php  # Registration