Building a multi-vendor eCommerce site in Laravel requires a few key steps. Here's a general outline of how to get started:

1. Define the requirements: Determine the features and functionality required for the multi-vendor eCommerce site. This includes features such as vendor registration, product listing, order management, and payment processing.

2. Create the database: Develop a database schema that accommodates multiple vendors and products. This includes tables for vendors, products, orders, and payments.

3. Develop the vendor registration and product listing functionality: Create a vendor registration form that collects the necessary information such as name, contact information, and product categories. Develop a product listing form that allows vendors to list their products, set prices, and upload product images.

4. Implement order management and payment processing: Develop a system that allows vendors to manage orders, view order details, and update order status. Integrate a payment gateway to facilitate payments between buyers and vendors.

5. Develop the frontend: Create the frontend of the eCommerce site using HTML, CSS, and JavaScript. Use a frontend framework like Bootstrap or Foundation to speed up development.

6. Testing and Deployment: Test the site thoroughly for bugs and ensure that all features and functionality are working correctly. Once testing is complete, deploy the site to a production environment.

Overall, building a multi-vendor eCommerce site in Laravel requires a good understanding of PHP, web development, and database design. It's recommended to work with an experienced Laravel developer to ensure the site is built correctly and meets all necessary requirements.