If you do not know the difference between a 20 year roof and a 50 year roof for God's sake leave that work to experienced contractors that can offer you a quality guarantee.

That is a Redflag 1.Without knowing the condition of roof, plumbing, exterior, foundation I question if 5% ex (,$400)  is adequate.

Also, I avoid flat roof, multi units with common HVAC, prop in flood zone, crime area, etc. as they are either too costly to fix that don’t worth investment of time n money or just can’t be fixed, period.Anything that comes mind to flip switch off for further analyzing that property or filter out before even begain to analyze?

MUCH better. can buy homes that cannot be financed normally. tarped roofs are gold mines!!! 

Here are the properties that have interested me (not sure if either are section 8):Duplex built in 2002 consisting of 3/2 1050sq/ft each for $94,900Currently both units occupied with $670/month leases (not sure of the lease terms).New roof in 2015, new Central A/C units in 2013 and 2015.Outside looks good, inside looks clean with decent kitchens (basic L shaped) with laminate counters, tile floor in kitchens, what looks to be berber carpeting everywhere else.

Roof, HVAC, floors, kitchen, bathrooms, paint.

We inherited some shady tenants that our property manager has gotten rid of and done a LOT of work to move in better tenants, but, on top of needing to be subdivided, it is currently nickel and diming us to death, plus we need two new roofs and all of the central AC units need to be replaced soon.

Then look for something that you can buy for lower than the market but rent at or above the market.Also find out what a typical rehab would cost you and break it down by major components (flooring, roof, plumbing, painting, etc). 

I expected to put in about $5-8k to update fixtures and some appliances.After the Home Inspection I've got three big concerns going forward: 1) Roof hasn't been touched since late 90s early 2000s.

If it was in a great neighborhood you could justify it as being an asset that will appreciate over time but with a sketchy neighborhood you are praying and hoping and that’s not a solid strategy especially when the ac goes out or a big plumbing problem or a needed  roof replacement