You can craft many items in the campaign, from armor and weapons, but you must have skill points allocated to Craft: [Category] in order to do so. You must obtain raw materials and/or schematics to do. The system is explained in more detail below:
Crafting Categories:
Armor
Weapons
Spellcraft (This is the existing Spellcraft in skills)
Potions
Siege
Traps
What you need to craft?
To craft items in the campaign you must have the raw material to do so. Most raw materials can either be found, salvaged, or bought. There will be unique materials and components you can find to add special affects or bonuses.
When you have the required materials, you can do one of two things. You can either find/purchase a schematic in order to know the quantity of resources you need. Or you can make a Craft [Category] skill check to see if your character knows how to craft that item that you want. If you fail to pass this knowledge check you have to buy a schematic or take a penalty to your Craft [Category] check to when you craft your weapon.
How long does it take?
Crafting takes time in the game world, there will be moments when you enter towns where you will have access to what you need to craft your items. The length of time is calculated from a Craft [Category] check and the complexity/quality of the weapon. You can rush your crafts but you will take a penalty on your Craft [Category] check for quality.
How are the stats determined?
I will determine final base stats of your item. Your will make your final Craft [Category] check to determine your characters success at making the item. This check will help determine the quality of your item, or if your character blunders and wastes the materials.
Can I get an example?
Of course you can! (Note: All data here is an example and does not represent what the materials actually do.)
Targen the Dwarf decides he wants to make a one handed waraxe. First he makes a check to see if he is knowledgeable enough in crafting it.
He has a Craft: Weapons skill of 15. His final roll tallies results in a 25. Crafting a standard waraxe is pretty common knowledge so he doesn't need a schematic. He finds out he needs 2 ingots to craft it and it will take approximately 2 full days to make it.
Targen the Dwarf has enough Darksteel and Obsidian to craft it. He decides to use Darksteel because it gives a inherent +2 to attack rolls against Goblins. He knows this because of a finding a tattered book on Darksteel. Though a Craft Weapons check could reveal if he worked with that material before and possibly gleamed what it might do.
Targen then makes a Craft Weapons Skill check to Craft the weapon. He doesn't have enough time craft it so he wants to attempt to craft it in one day which raises the difficulty of the check. His skill check results in 20. Luckily since it is a simple weapon with no other enhancements he makes it without too much difficulty. His weapon now has the base stats of a common waraxe, but with a +2 to attack rolls against Goblins.
If he had extra time, he could lower the difficulty of the check or opted to use extra materials to try and get a boost to its effect or find a new affect by combining materials.