Feel free to take mats from the guild bank to craft stuff if you can.
The main thought of the bank was to store items that might be needed by others in crafting and sorts. If you need some items that are not in or have withrawn the maximum number of items for the day, grab me or an officer so we can withraw it for you.
Items you create may be deposited back in the bank or sold at AH with the profit deposited.
Remember, the cash in the bank are for your repair bills in future guild events so dont be ego