Like has been mentioned; do you have a history of wood work, metal work, crafting, art work or any other prerequisite leading up to building a gun? Do you have the level of patience to stick to a small detail even if it takes days to complete correctly, a buttplate or entry pipe come to mind.
The reason I sound like gloom and doom is I teach bow making. Almost always my students haven't done anything crafty in their past but are "enchanted" with the prospect of making their own bow. None of these guys ever complete a bow, they get disenchanted with the work involved, don't remember the process I teach them and get lost on what to do next. I teach for free, perhaps if there was money involved they would stick to it.
My progression was; general handyman, duck carver, bow maker, flintlock builder and I still found flintlock building very challenging,