First - look at the Tax Role, this is a great starting point to help determine the property value based on land only (dirt). Then add either plus or minus with a CMA created on Lot/land in same neighborhood/zip code/town.

Second - you'll need to determine if the home is either a Custom built or a Spec home. There is more value on a Custom Home then a Spec Home.

I also use a square foot starting point of $50.00 a square foot. If it's a Custom Home I use a $75.00 square foot - depending upon neighborhood / area.

Third - Just as if you were trading in a vehicle you'll need to add or subtract values for additional items. Like a vehicle trade-in you add for A/C, Automatic Transmission and Low Mileage. It is the same in Real Estate. You add in for Granite Counter Tops, Title Flooring, and Land Scraping. (Plus other features.)

Best source (I've found for this information) to get estimated improvement values is: http://www.lowesmoving.com/, http://www.realtor.org/ or http://www.costvsvalue.com/.