While there is a similar instructable on how to make your own root beer, there isn't one for ginger ale. I've made my own ginger ale for years, and here's how.
Step 1: Ingredients/tools
--1c sugar (or less)
--small piece of ginger root
--a grater (microplane or fine holes) or food processor/chopper
--an empty 2L plastic (important) bottle
--around 2L of fresh water