Statistics for Real Estate Appraisal

I'd like to analyze sales of properties to determine which features are relevant and then how much they contribute to the whole. For example, I'd like to look at a population of several hundred comparable sales of houses to determine if the addition of a swimming pool does add value, and then determine how much it adds. I'm able to complete a multiple regression analysis in Excel but don't know how to interpret the results and if that is even the proper method to do what I want.