Making Etchable PDFs in linux
Eagle's professional edition layout tool can do 64 x 64 inches.  Since it seems that you know Eagle, that's the simplest option.  It is not the cheapest option, but only because it's not free (as in beer).  

Like most powerful tools, gEDA has a significant learning curve.  It's not impossible to understand; it's just not as intuitive as Eagle.  Keep trying.  As with many open-source projects, features come before documentation, so many of the tutorials are out of date. I suggest you follow the geda-user mailing list to get the most current information; it's quite active and the devs want to help!