Is the city doing one area at a time and making sure everything is up to code proactively? 

If it is one lot/parcel and zoned for two units, meets health and safety codes should be good.  

This should be in the written report.....some guys color-code the problem items.

@Nicolas Whitman the cash buyer list from Propstream has been pretty good for me; I can give some cheat codes when it comes to working that list. 

You could do layers to color code different priorities. i also delete or change color of the property marker once I have seen it.

How many tenants are current in their rent.Other due diligenceCheck for building code complaints/violations pendingLook at rents in the area (within a couple blocks) Look at amenities, look at crime rates.

You’ll need some code compliant (architect) plans before you can get any kind of accurate pricing. 

Building code didn't exist, so you could end up with major structural problems.

Sales price/sqft broke multiple family record for the entire zip code at the time.

If I were you I'd start meeting with local architects and contractors just to see what is possible and the costs involved.Have you checked with codes and zoning yet?