Cage Expansion

Say you have a cage thats 8x12 and you need to add another row, so your cage now becomes 14x12. Now the cage installation is per linear foot. so if they are bumping one of the 12 feet walls out 6 feet. What do you think you should be charged? 6 + 6 + 12? or 6 + 6 + 12 + 12 OR 14 + 14 + 12 + 12?

Also what do you think the legality of a company charging you for a 6 + 6 + 12 + 12 expansion when the other 12 foot section is never touched? Charging for a service that isn't ever done?