Jigoshop / E-Commerce Developer

I have a WordPress e-commerce site in development, the plugin used is jigoshop. I would like to customize certain elements of jigoshop to suit our needs. When you enter a variable (the variable is size) product through jigoshop, and specify that you have one item in stock, jigoshop thinks that you have one item of each variable. The desired result: The site is for fashion design, there are different designs/dresses, a picture of each design is placed as a product, but for some designs, there is only enough fabric to make one dress. When someone orders a size small for a certain design/item, I want the item to show as out of stock for all other sizes. This is the main element that needs customizing, there are small minor things here and there as well. The chosen contractor will be briefed fully on what needs to be done.