This CrossFit Journal article, originally published in 2006, provides instructions on building a do-it-yourself custom CrossFit plyo box with slanted sides.

The online L1 course — available to those who hold a current CF-L1 or CF-L2 credential which they need to revalidate — is comprised of lecture-based and interactive instruction on the fundamental principles and movements of CrossFit, a 50-question test, and live Q&A and instruction with CrossFit’s top coaches.