I often read this board but haven't written in before. And I don't mean to criticize, but I am really wondering, how can a book estimate like this be of any value? It seems to me that the cost could vary so widely that an average estimate like this doesn't mean anything. for example, a "4 foot wide" dormer may have a front wall that is 6 ft high, or 3 ft, it may have a ridge line that is 4 ft long while another may be 10-12 ft. And one might have t-111 and 3 tab shingles, while another has top grade redwood siding and a slate roof. And what about size and quality of window? I guess my question is: what goes into developing a number like $2200, and what good is it? Again, no offense intended, I am just trying to learn. Thanks.