This skill encompasses several categories, each of them treated as a separate skill:
Craft skills are specifically focused on creating objects. To use a Craft skill effectively, you must have a kit or some other set of basic tools. The purchase DC of this equipment varies according to the particular Craft skill.
To use Craft, first decide what you are trying to make and consult the category descriptions. Make a Wealth check against the given purchase DC for the object to see if you succeed in acquiring the raw materials. If you succeed at that check, make the Craft check against the given DC for the object in question. If you fail the check, you do not I make the object, and the raw materials are wasted (unless otherwise noted).
Generally, you can take 10 when using a Craft skill to construct an object, but you can't take 20 (since doing so represents multiple attempts, and you use up your raw materials after the first attempt). The exception is Craft (writing); you can take 20 because you do not use up any raw materials (and thus no Wealth check is required to use the skill).
Note: Skills provide the tools to keep the action moving between combat and in noncombat-oriented dramatic scenes. While the Craft skill could be used to make money, it has more application as a tool for characters with a scientific focus. Plus, the cost of hand-crafting an object in the modern world usually winds up being higher (both in time and money) than simply buying the same object from a retail outlet.
Many projects covered under the Craft skill take hours to complete—some take 24 hours or more. The time shown is the number of hours spend working, and these hours may have to be spread over a period of several days (or longer).
In general, a character can spend up to 12 hours a day working on a project-but that doesn't leave much time for anything else. In a pinch, a character can work longer hours. However, any character working more than 12 hours in a single day must make a Fortitude save (DC 15) or become fatigued. The penalties for being fatigued apply to any checks made for the projects being worked on.
A character who works more than 18 hours in a day automatically becomes fatigued (no save allowed). A fatigued character loses the fatigued condition after getting a full night's sleep (8 hours).