I followed Sandor Katz's approach (start a ginger bug with a cup of water, a tablespoon of sugar, and some grated ginger). It usually takes me a day to get that bubbling away. My recipes are fairly general: ~10-12% sugar solution, with enough roselle (or ginger, or ginger/turmeric, or mint/lemon) to give sufficient flavour. Ginger I usually boil with the water to extract more flavour. Mint and roselle I just steep in the water after bringing it to a boil. I almost always add some lemon, as that always makes it taste better. I rarely measure these amounts (apart from the water & sugar), but tend to go heavy on ginger if I'm using that.