Roofs are $10-15,000 for a typical duplex where I live.  

3. requiring heavy amount of rehab (siding, foundation, roof, HVAC, appliances)?

I signed up 2 days ago, and now that I am using it, I am finding certain aspects of the software very frustrating. 

So this doesn't seem right to me...if I see "new construction" as a buyer, I:a) assume the home has never been occupied, andb) that licensed contractors were used to build all aspects to state code, to offset the lack of required inspections.I know homeowners can do their own work, but shouldn't that imply occupancy and be listed as previously owned home vs. new construction?

Common problems are sewage backups, mold, infestations of rats, and other pests, faulty wiring, roof leaks and it violates the city’s building, health and fire code poses health and safety risk.

These other aspects of the strategy seem great, really reduces the chances the neighborhood is just going to tank in value or something I would think, though I suspect fitting a curve as opposed to just using the mean may be a bit more effective and less risky.

Roofs and 'lesser' critical home hardware like HVAC, AC, plumbing and non functioning lighting and electrical. 

A great agent will also invest in home, pest, and roof inspections to remove doubt in a buyer's mind prior to making an offer.

Construction materials: Frame, no basement, roof: asphalt shingles, Floor: Carpet on stairs and bedrooms, LVP: Kitchen and living room.

No leaks from roof or in basement.