How to evaluate capex/deferred maintenace before purchase

[Jeff S.]

I'm in the learning phase before buying my first rental.  I'm thinking I will do a fourplex, owner occupied.  I've found a target neighborhood where the numbers (1% rule, 50% rule) seem to work and the tenants are desirable.   The area is all boxy, mid-1980's roughly identical fourplexes. It seems that that age is right around when the effects of good/bad management begin to really show - some units are a little ragged, some pretty nice.

What I want to learn is how to be precise about capex estimating. I can think of a few ways:  please tell me how YOU recommend estimating capex.

My ideas:

1) Just use a trusty fixed % of purchase price. (How to choose that % for my market?)

2) Look at records from seller. (Can you trust this at all?)

3) Look at records for similar properties (How do you access this?)

4) Ground up approach: (cost of roof)/(useful life of new roof) + ditto for HVAC, paint, landscaping, ... 

5) Similar to (4) but inspector determines remaining useful life of roof, paint, HVAC, etc. and timetable for updates is established.

6) Other?

Several of these require that you have a specific property in mind and under contract, whereas (1), (3) and (4) four would work for a blanket area of similar candidates.