Is there a list on the game showing whats needed to make the HRE? Or is it a stumble around and hope you make all the right decisions kinda thing?
There's a series of imperial decisions, it should be on the wiki
http://www.paradoxian.org/eu3wiki/Forming_HRE there you go
You need to be someone like Burgundy or Austria, become the emperor, stay that way and get involved in every war you can involving members of the HRE to maintain the imperial authority necessary to enact the reforms
if you do it its the most powerful form in the game, beats the crap out of germany, the form I previously thought was godly
Also, it has a tendency to cause the game to bug out, that much resources, manpower and territory cause problems. Once you pull it off the games over anyway because no one could possibly beat you