question regarding items

[KidsEatFree]

How would I set up a trigger to make items cost lumber to attack. For example, a unit picks up an item (pistol), and I want the item to use 1 lumber whenever the unit attacks while holding the item. When the player controlling the unit runs out of lumber, I want the unit to stop attacking. How would I go about setting up triggers for this?

Thanks in advance for your help

edit: Nevermind I figured it out.