@Anthony Jeffers, correct. Lenders/experienced investors will typically use comparable sales to determine how much they will lend you vs. using CAP rate to determine LTV. Remember: if you default the lender has to turn around and SELL it, and usually a default on a loan indicates the property is being run poorly and may be in a shambles or disarray. Their last desire is to own the property and manage it, regardless of how awesome the CAP rate is. Your boosting NOI $10,000 annually on an 8 CAP 10 unit complex won't increase the value to $1,100,000. Maybe among smaller Buyers some will look at it that way, but traditional lenders or institutional investor won't. They're concerned with, "If Anthony drops off the face of the earth, what can we sell this for quickly?" And since most small Buyers are going to need traditional lenders or institutional investors underwriting their purchase, they too will have to use those same guidelines for all intents and purposes. Which is why you want to look at bottom line cash flow as I mentioned in the final paragraph above.
@Reggie Desir, see the above paragraph. Per my original post, you can run a CAP rate analysis for your own personal, internal purposes comparing apples to apples on anything from a SFH up to a medium size MF as long as you properly account for all expenses, including your own donated labor, equipment and materials. But to reiterate: no lender or large investor who will underwrite this venture will value it that way. I learned this the hard way as I was running CAP rates for months to find good deals. I finally found one (20-unit MF complex, price $1,1 million), got it under contract, then the lender said, "Nope, comps won't support it." Institutional money wouldn't touch it either. Too small of a fish to get them excited.
I know, I know, I know...many folks on BP preach CAP rates and forced appreciation, etc. If you could dig into their smaller deals and see how they really happened, my guess is you would find CAP rates are a second or third tier concern behind comps. Either that or they have access to vast quantities of private capital from investors who only care about cash flow and the Buyer finds something that cash flows well that also runs a decent CAP rate analysis. This leads to conflating the two concepts and the Buyer thinks it's all about the CAP rate rather than the cash flow. The two are often positively correlated. Anything 9 CAP+ should cash flow well as long as it's not overleveraged or in terrible condition, but it's the cash flow, not the CAP rate, that makes the deal happen with these smaller properties.
My experience in the world of MF says anything below 50 units is considered "small". Medium is somewhere between 50 - 100 units. Over 100 units you're talking large....maybe 200 units in some markets. Anything between 5-10 units is going to be straight comps and may be based on using multiples of single duplexes that have sold in the area. Unless your market is considerably different than mine, 5-10 unit buildings rarely come on the market, so the appraiser will take 2 - 4 plexes and multiply by the number of units to get a reasonable guestimate of value.
As always, this analysis is brought from my market perspective and experience. Others may feel differently or their markets may need numbers adjusted. I'm from a Mid-West town of 170,000 people where real estate is relatively inexpensive compared to the coasts and other big cities like St. Louis or Indianapolis. The thing you can buy here for $1.5 million might sell for $3 million elsewhere, and that changes the game with lenders.