What other cost factors might you include in such an economic analysis?

The proposed small office building in Example 3-2 has 24,000 net square feet of area heated by a natural gas furnace. The owner of the building wants to know the approximate cost of heating the structure from October through March (six months) because she will lease heated space to the building's occupants. During the heating season, the building will require roughly 60,000 Btu per square foot of heated area. Natural gas has 1,000 Btu per cubic foot, and natural gas costs S9.00 per thousand cubic foot. What will the owner pay to heat her building?