The build cost would be a little higher because i would use foam in the exterior walls and also use insulation in the interior walls for energy saving and sound dampining.

I make sure they're well insulated, have replacement windows, spend more on nice flooring that looks great (plank style / wood-look porcelain tile, hardwood or click-together LVT planks, not peel-and-stick squares). 

Quick tips…✅ Everyday Homeowners - track all home improvements as you could qualify for energy efficiency home improvement credit - new exterior windows, new central A/C, new hot water heater, new insulation material.✅ Investors - Keep detailed records of ALL rental property expenses to reduce your taxable income - helping your CPA spot additional tax saving opportunities.Imperative to use a CPA who is well versed in Real Estate tax code.My CPA is just that - DM me to get his contact information....

Quote from @Blake Van Ness: Hello i'm working Insulating my garage.

Only tankless water heaters, extra insulation, heating/cooling, etc....

You are correct that insulation is almost certainly a bigger bang for the buck in a heating climate.

I got a quote for 8K sft retail from a construction company for around $120/sft, this includes site prep, utilities, metal building erection, exterior finishes, interior insulation etc (basically build the shell from scratch).

We still have to disclose that I'm a licensed broker but the offer coming through another agent puts a layer of insulation between us that makes sellers a little more comfortable.Finally, I like seeing my agent get paid.

Unfortunately, she frequently turns it off to save on electricity, which exacerbates the issue.i have also sent her extra radiator heat so can just plug in , but she refuse to use because she has to pay high electric bill.She complained about the unit's insulation and requested that we install an additional baseboard heater( whats the use if she doesn't turn on the heat) .

These losses depend on the layout and geometry of the system (ductwork, piping, etc) and the insulation used, the ambient temperature that these ducts/pipes are traveling through, the temperature of the air or water/glycol mix etc...