Keep your Information Current
Once you verify your facts, you can select your commercial real estate comps. Use an address as close as possible to your prospective sites for accuracy when comparing neighborhood demographics, flood planes, etc. Various district lines and land developments can change often so stay up to date.
Prices per square foot
Pricing by the square foot is time-honored. This method of commercial real estate comps valuation doesn't exactly account for choice location. While rent is obviously an important factor, it is certainly not the only influence on your PSF. Don't forget about your utility usage, taxes, CAM, etc.
Quantitative vs. Qualitative Data
You have the numbers and you've compared them, but now come the more unique characteristics. The quantitative data may be difficult to qualify relative to your list of commercial real estate comps. To compare apples to apples, consider developing a standard for the features you are looking for to weigh against your list.
Consider these factors for your fair market determination:
a) Highway Accessibility
b) General Space Condition
c) Customer Proximity
d) Amenities
e) Parking Ratios
Is your space close to restaurants, schools, an airport, or day care? How does it stand against the condition of other buildings in the area, or other units in the building? Is it noisy and busy, or quiet and calm?