Books about investing in medium-sized mutlifamily

[Wes O'Hara]

I'm having a very difficult time finding a useful book that discusses finding & evaluating medium-sized multifamily properties.  So many are geared toward single family.   I've owned a 4-plex for nearly 20 years and want to take the next step.  I'm also looking to go out of state, so a book that touches on that would be a major bonus.  Any recommendations?