If you start with pre-assembled kits, they're really quite difficult to screw up, and the results are usually quite drinkable. The pre-assembled kits are usually 5 gallon/19 liters, although 1 gallon kits are available as well, but cost goes up (per yield).

The next step after would be taking recipes, either from the kits you already made, or found elsewhere, and assembling the ingredients yourself, tweaking where you want to make a change.