A basic homemade sports drink only needs a few ingredients: carbohydrate, electrolytes, flavouring and water.
For the carbohydrate, a combination of maltodextrin and fructose is a popular choice for endurance sports. Sodium citrate or salt can provide sodium, while flavour powders or other food-grade flavourings can make the drink more enjoyable to consume.
The amounts you use depend on how much carbohydrate and sodium you want per bottle. Start with a simple recipe, test it during training and adjust the strength and flavour to suit you.