Crafting mundane items progresses at a speed of 5 x your proficiency bonus gp per day; you may not craft an item unless you are proficient in the tool required to create it. The cost of the materials remains the same (half the total cost). This does not affect the crafting of magical items. Any one whom is proficient with the tools required to craft an item may assist in any crafting attempt. They add half of their proficiency bonus to yours for working out how many days it takes to craft an item. For example, two blacksmiths are working together to create a set of full plate armour. Normally this would take a level 10 Blacksmith 75 Days to craft by their self. If a second smith helps this would instead make the armour take only 50 Days to craft.