Custom doors can cost a lot and often dont know how well they will fit. I didn't want to take the risk of having someone else build them and have them not fit to my liking or buy some standard ones and risk the same thing and make additional modifications.
The same conciderations were made in making them. if I were to measure the opening, as most custom door makers would do, there is a chance that when the doors are installed that the lines wouldn't line up and things look a little off. I chose to make the metal frame in the door opening so that I was guaranteeing a perfect fit.