I don't think PCS even offer the potential for sending in your own laptop case? Your best bet imo would be to purchase one from ASUS really if your set on that style.
Unfortunately the big issue with laptops is you are limited with the hardware you can put inside of it due to its design. Not all laptop motherboards for instance will fit in all laptops (obviously?) and subsequently not all components are compatible with different laptops either for the same reasons.