Most of the "not so good" ones I had to find out the hard way, having spent extra time, effort and $ to be unpleasantly surprised.I have already went through all the permits and old records looking at microfilms for hours at the city's archive office.But I still have a lot of questions that I believe this person can answer.  

Check with the department of buildings to see if they have the blueprints in their archive.

I have looked through the archives and there are a few threads on this topic but all that I found were really old and outdated. 

I hope you can go in the archives of BP to my past posts concerning this topic, I know greed usually prevails but be warned.

I've been doing a lot of research and reading archived posts here.

The following two images are actual calculations we did for the 6-unit property and I pulled these from our archives.

I'll definitely archive all of the great information.

I will search the archives to see if I could find the related posts. 

What happened to the BiggerPockets app on the itunes store?

You can archive them on your cell phone to keep the logs if that helps.