To make the armor that has already been made by the workshop, the blacksmith needs to take the pattern, adjust the size and make the set. Timing of order is known in advance.
When the customer needs armor made according to his/her sources, the blacksmith has to make a 3D model of foil or something like that. Only then he can start production of armor. Needless to say, such procedures require additional money, so the armor will be more expensive.