Helps with your debt to income, better opportunities at cash flow, and typically requires less down to purchase.In regards to challenges, I usually build in an extra 10-15% to deal with things that I can't see behind the walls, including dry rot, electrical or plumbing issues, etc.

Licensed with permits ~$3,250.HWT standard gas single family low efficiency without exhaust retrofit $900.Sand and stain hardwood floors, natural stain $3 per sf.Paint interior walls, ceiling trim and doors 3 tone paint scheme 2 coats $3.20 per sf (floor area cost includes paint)Click lock LVT flooring install overlay inclusive of prep and quarter round $4.50 per sf (materials and labor)Asphalt roof installation 3/1 - 800 sf bungalow with 2 layers of shingles - ~$7,900Standard porch cap replacement with 2 new precast concrete steps ~$2,500Used stove or refrigerator delivery and install $350New stove or refrigerator delivery and install $HD model specificUse this as a general guideline. 

It had some good architectural features that people loved, and the original plaster walls downstairs were in great condition, not even cracked.

Water is now leaking through the ceiling into my tenant's unit, and it's worsening with every rain also the neighboring unit has sever water damage (like a pool inside and it is owned by the HoA) and water from it leaking very dirty water from the shared wall to mine.

Are you aware that over 80% of Wall Street / Stock market companies DONT last that long?     

they said around 90% of market value.I tried to get them to understand that this property needs a LOT of work, almost a full gut, some holes in walls (small) old carpet needs to be ripped up, i mean like the works on this thing, you can prob get away with touching up the kitchen since its real hardwood and the bathrooms as well but this prop needs at least 80k.Found out owner actually owes 140k on property, and zillow is zestimating it to be 127k.

Expect to remodel kitchen and baths and put new floors down, paint, knock down a wall to open the floor plan. 

The only big issue I ran into is on of the basement walls needed extra support, I don't think a newer build would have that issue. 

Use of Euro-style wall units for air-con.. 

In our student houses we use a programmable thermostat, but our building monitoring system has its own sensors and can override the wall thermostat and will not allow the temperature to get below 10C (50F) ... we are presently testing a new software load that will also prevent them from cooling the house too far in the summer.