@Mendel DeitschAs you pointed out cap rate is a metric to measure some kind of return (ROI).

I use 20% of the gross as an initial measuring tool.

If you want to replace just the glass as I did recently measure the glass and go to Menards, $35.

Also, Las Vegas has the further to go to reach pre-crash peak prices than any other major city.InventoryInventory is measured in months of supply.

- What other key measurements do other suggest?

It's been really valuable, and I appreciate your time.After the options and considerations, we settled (amicably) on the tenants paying for the replacement door glass panel, and my handyman installing it.I love the measured responses here.  

County is usually closer to accurate, but really the only way to get the accurate size is to go measure it yourself.

@Harrison CookYour post kindles lots of questions.In the "good old-days" most heating systems were vastly oversized for the building they were heating - energy was relatively cheap, insulation was non-existant to poor ... so it was easier and safer to {drastically} oversize.Today, while energy {in North America}  is still relatively cheap for the moment,  we have a much better understanding of how to make buildings more efficient {though you might not think so looking at the construction industry in the U.S.A. and Canada}  and there are often more cost-effective measures than simply replacing an old, over-sized heating plant with a new, over-sized heating plant.You really need to - or at lease should -  perform a heat load analysis to properly size your heating system, a component of which, is determining the rate of heat loss of the building envelope.  

When this is measured and compared accordingly this can be become a six figure matter of difference.  

Occupancy is not a particularly valid measure.