A cost approach is done on new construction. You will need to figure the value of the land, using not only your property, but other comparables in the area that have sold within the last 6 months. This assumes that all necessary improvements (ie utilities) have been accomplished and the lot is ready to build on. That will establish the value of the land. Then you will need to figure a cost to construct the home based on the per square foot figure that your builder gives you. If this is not available then you can look at other new construction of the same quality as the home you'd like to build and use that cost per square foot figure. Be sure to use sold prices of other similar homes, not listing prices. Add that to the value of the land and you'll get pretty close to what the bank's appraiser will estimate.