Plumbing drain pipes - Plastic/PVC is ideal, cast iron means you will likely have corrosion inside of them and have more maintenance costs involved.

It looks like the side of the home (wall) already buckled.The top photo faucet already tells me about the corrosion and possibly plumbing issues under the home.

Model number is: XG40T06EC36U1) Our general contractor recently spotted some corrosion and leak on one of the water heaters.I'm not sure if this issue is related to another issue mentioned by our home inspector on the inspection report: Venting pipes for Both Units also showing improper pitch to chimney stack. 

I had a plumber somewhat recently say that due to corrosion and the age of the duplex, he estimates I'd have to re-pipe both units in 5+ years, briefly estimating the job to cost $12k PER unit. 

Plumbing - Corrosion and/or oxidation was noted on one of the PEX crimps under the kitchen sink.Over time, this can increase the change of leaks.

I could paint it to protect against corrosion.

Then there were the 3/8 Cu feeds off 3/4 inch main lines so corrosion jammed them up over the years.

If you are close to a beach, is there salt in the air that can speed up corrosion? 

If you have a tenant that is dealing with corrosive chemicals, it can eventually eat away at framing members so be careful on who you lease to and what their plans are.

Using the snake through the roof stack would still put us at the same clog.I don't know if it would be possible to open up the access panel and try to disconnect the drains that way and get something in the pipe to try to grind out the corrosion.