I guess it would be similar to rituals in implementation.
First a player would need to take a feat to become trained in whatever area of craftsmanship.
Metal Working
Leather Working
Wood Working
etc.
When crafting an item, you spend a specified amount of time and pay the 'component cost'. The creation rituals in the PHB don't require skill check, so lets say that mundane crafting doesn't require them either. If you have the necessary training to create an item, all you need are the materials and the time.
*edit*
More.
Like rituals, you would also have to be a certain level or higher to craft certain items.
Lets say...
Simple Weapons: Levels 1-5
Military Weapons: Levels 6-10
Superior Weapons: Levels 11-15