Its ironic because my rentals are the nicest homes in the neighborhood. 

I had to replace the old cast iron sewer line in the basement.

However, we have yellow iron on the ground.  

You do not say whether the pipe is Cast Iron or not.

So I guess one has to have an iron glad contract written up by a good real estate attorney then documented at the county level. 

Property Cons:The property has original knob & tube electrical wiring, cast iron plumbing, needs a new roof (estimated at $18K), major work to the original wood siding & windows (estimated at $40K – need to stay within Historic District requires), and extermination of pests (estimated at $5K).

No one told me because, I hope you guessed it this time, previous landlord constantly threatened them with a bill and/or eviction every time a clog arose.It matters in the legal sense that the clogs are from root intrusion on a 75+ year old cast iron sewer line, but it doesn't matter in a practical sense.

Metal roof is fairly generic and can cover a variety of roofs - brass, bronze, copper, iron, steel, aluminium, etc.Around here a metal roof from the 1940s would most probably be a {corrugated} galvanized steel roof.  

Welcome to BP @Hylton Irons and props to you for starting early...

There’s a hotel data company called STR (ironically NOT for short term rental!)