Crafting an item requires a Craft skill check equal to the DC listed on the item. You make an amount of progress towards an item equal the result of your check in silver pieces. If the amount exceeds the amount of the total cost of the item you complete it. For example a Short sword has a cost of 10 silver and has a Craft DC of 12 (Trained). Seraph has a bonus of 7 to Craft Blacksmith, and rolls a 10 for a total of 17. She exceeded Craft DC and makes 17 silver worth of progress and completes the item since her total was more than the total cost of the item. For every 10 you exceed the Craft DC by you make double the progress.
When attempting to make a weapon of Skilled quality or higher you add +5 to the Craft DC of the item for each Proficiency level. Expert would add +10 for example while Master would add +15. While crafting over long periods of time you may choose to take 11 and add your bonus from crafting. If you are able to add advantage to the roll for the entire amount of time you instead use 15 as your starting base. You may only make a level weapon in which matches your proficiency level in crafting.
Skilled level Weapons gain a +1 bonus on Strike Rolls and Ignores 1 Damage Resistance
Expert level Weapons gain a +2 bonus on Strike rolls and Ignore 2 Damage Resistance
Master level Weapons gain a +3 bonus on Strike rolls and Ignore 3 Damage Resistance
Skilled level Armor gain a +1 bonus to Block Defense rolls and gain 2 additional Damage Resistance
Expert level Armor gain a +2 bonus to Block Defense rolls and gain 3 additional Damage Resistance
Master level Armor gain a +3 bonus to Block Defense rolls and gain 4 additional Damage Resistance