The most information in this thread is not accurate.

I am not in your area, but I invest in your area and around the region of central California.

and why are they needed in this deal?

And the reason why your "tale of two halves" will play out as you described.Demand:  This has actually been high almost all along, but rent growth hasn't materialized in response due to high levels of new supply. 

Then you can read a more in-depth book like The Book On Rental Property Investing by Brandon Turner or The Unofficial Guide to Real Estate Investing by Spencer Strauss.2.

@Jeff Mooney Hey Jeff where in Central PA are you looking?

Affordability is one of the biggest challenges in today’s housing market.I believe smaller, more dense units are part of the solution:1) Buyers can only afford smaller homes in today’s economy.2) Denser units maximize the land available, increasing housing supply to help offset demand and ultimately bring costs down overall.It’s not just about building more, it’s also about building smarter.What are your thoughts?

What are some of the best areas or even zip codes that would be good to buy a rehab property? Looking into Philadelphia, Bucks, Montgomery county. Thank you!

Tell them you want to get into investing and ask them if they know of anyone who might be interested in seller financing. 

Quote from @Jules Aton: I started investing in my late 20s during early 90s in up and coming inner city neighborhoods.