If you see a pattern (which is common) of distress within the units then it's easy to multiply across unit types.  

-Be extremely careful about deferred maintenance, items adds up very quickly when multiplied by 172.  

This is also multiplied through the subs, the subs are doing the exact same thing, prioritizing the jobs that are profitable to work on and deprioritizing those that aren't.

I personally don't change my bids for a 750k property or a 120k property (as in, I don't use a different multiplier).

Our duplex is almost as much as our quads, and if I multiply our SFH times 4, that is much more than what we pay for the quads.I am evaluating a multifamily deal in Huntsville, AL and my insurance guesstimate is way over what was provided by the seller's agent.  

Let me share a story on a CL laborer "GIG" hire.Several years ago I had to create a few drain fields for my swimming pool, and at the end I end up with a big pile of excavated sand that needs to be disposed of.Imagine how much sand a typical bathtub will hold, well multiply that by 5.I posted an ad on CL, posted a picture of the big mount of sand, gave the estimated volume how many cubic feet, and asked for a lump sum quote to come pick it up and dispose of it. 

On an apartment complex where you can come up with a typical amount per unit and then multiply by several units, then maybe yes.

so if i am really bad with estimating repair costs, could i just do a 1400 sq ft house and multiply it by $40?

If the house is rectangular, measure the length and width, add them together, multiply by 2 and then multiply by the approximate price range I gave.That is for a perimeter French drain system; as others have pointed out, placing a sump in the middle of the floor is not the way to do it, putting the sump in the corner gives you usable floor space in the middle of the basement where it is most useful.  

An appraiser will have a multiplier (the Market Cap Rate - specific to the area and condition of the property) he will apply to the NOI to determine a value for the property.