Building a Custom Shopify App: A Step-by-Step Guide is a comprehensive blog post that provides a detailed roadmap for creating a custom Shopify app. It covers the planning phase, setting up the development environment, coding, testing, submitting the app for review, and launching it on the Shopify App Store. This guide also includes helpful tips and resources for developers who want to build a successful Shopify app that meets all of Shopify's requirements and guidelines.