Get the Whitepaper called Metasploit – The Exploit Learning Tree. Instead of being just another document discussing how to use Metasploit, the purpose of this document is to show you how to look deeper into the code and try to decipher how the various classes and modules hang together to produce the various functions.
You can download it from the following link: https://packetstormsecurity.com/files/download/123015/metasploit-the-learning-tree.pdf
Source: https://packetstormsecurity.com/files/123015/Metasploit-The-Exploit-Learning-Tree.html