Rational approach to multi-family physical inspection?

[Michael Klinger]

What would fellow investors say is a rational approach to having a (say) 50+ unit building inspected?

I am not particularly interested in knowing about loose outlet covers and those kinds of nit-picks I've seen in inspector reports. I would like to know if the roof or if the mechanicals are all going to die tomorrow.

Would you have a random sample of units inspected? Rather than every single units. Cost/time being the consideration.

Also, do you typically personally tour every unit? Is that normal/rational? Or overkill?