I have been a property manager for 15+ years as well as know all trades (roofing, minor plumbing, minor electric, drywall, paint, carpentry) from my years of working on homes.

It was built in the early 90‘s , its been maintained decentlyWill require a new roof in a couple of years Drainage issue under the home , will cost roughly $2500 to correct It was rented for a short time 3 months ago for a period of 3 months.

It will increase the perceived value and the appeal of the building to a new owner...it is nice to know there are new pipes, so it might make them more comfortable buying your building.... but because it is an unseen it will not exactly increase the actual value nearly as much as something like a new roof that they know there is a limited lifetime on,  and much less than a new kitchen would increase.Most owners never consider the fact that they will ever have to replace all the pipes so in their mind you are not saving them any money and certainly not making them any money....so it doesn't change the math.

Does anyone have any good referrals for contractors (metal roofing, carpentry, electrical, and plumbing) that are out in (or get out to) Packwood, WA? 

The flip side however, is I've gotten new roofs, siding / painting, landscaping, etc... when it comes to external maintenance that was handled by the HOA.But what I'd caution you over even more than HOA fees, is the CCR's...

I live in one  unit and want to split it in half and rent the upper floor, and build out 4 more units in the unfinished area that already has a roof , exterior walls and concrete foundation.By my estimation I need $275,000 to do the build out.

I bought a triplex that has a flat roof. 

OH yeah,  STR has the same issues as buy/hold -   I just got a call for roof leak after the first major rain in California.   

Are there walls to hold up the roof?

I would suggest as many doors as you can buy under one roof