They have their drywall guys, their carpenters, floor guys, roof guys, etc. 

Replaced roof, updated electrical wiring, radon mitigation system What was the outcome?

This 4plex is in a class C or D neighborhood (not exactly sure which) but my realtor and I saw the potential in it due to the cash flow/COC numbers we calculated and the fact it had a ton of work done to it in 2017 to get it to decent shape (all new electrical, furnaces, HWHs, renovated apartments, new roof, all doors and windows, etc.) 

If rates go down just another percentage point, that's what I'm hoping for by year-end, prices are going to go through the roof...Everyone will come out and buy.

In one case I heard of, the city told a homeowner that he could not pull an owner-builder for a roofing permit.

Built another smaller 1600 sq ft house with open air balcony for a roof for $130,000. 

I personally don't know much about that market but I have worked with a lot of people in Florida that are investing in Detroit.Some newer challenges in Florida are insurance costs going through the roof.

Be sure to get information about the age of the capital expense items (roof, HVAC, water heaters, and sewer line as well).

If your roof lasts that long.

One, you now have double the doors, w just one roof.