Congrats on making your first post here in the Community. Allow me to give you some insight about why you're not able to get a maximum number to build from.
The reason why you're receiving a zero instead of a number for the maximum is that you need to have an amount for the QTY on hand associated with the item called DOTS-006. Once you enter an amount for the QTY on hand for that item, then you'll be able to see a maximum so that you can combine items to build finished goods.
See, there was no need to worry. The Community is always here to have your back. Here are a few articles that can help you out with your inventory: