I had a duplex built in 1880 and when we took out the bath tub, we found that two floor joist were cut out for drain pipes.

The decking drains great. 

Primary bath shower doesn't drain that well, and quotes to fix it are $10k. 

Need to go conventional with MANUFACTURED home (double wide after 1976) The county or city may restrict the type of foundation: pier, auger, blocks, concrete BUT it must be permanent.

The inspector's main concern is that the connected roof does not have a drain and seemed to rely on my roof's drain and he recommended to have them sort that out.

Getting those to drain well eliminates the mini ice rinks and usage of salt. 

I have done a rental credit with a different tenant in the past for a different issue, they ended up breaking their lease anyway and it was really money down the drain in that instance.  

Something else for your location would be to remember to close any water valves to exterior hose spigots, and drain any water in the line past the valve by opening the spigot.

You will have overruns as well as things come up that you did not expect and it will drain your finances.

I used to assume that the PVC drain pipes were not susceptible to roots or other issues like the old clay metal pipes.