cost to put in a dormer window in the roof
1 Hiring someone to build a small dormer the width of a single-or double-wide window can run $2,500-$5,000 or more, depending on size, the slope of the roof, the strength of the existing roof support system and other factors.2  A larger, more room-size dormer can run $5,000-$20,000.3  Prices may vary considerably by region.ypical costs: 1  The Family Handyman magazine estimates it takes about $1,800 in materials for a do-it-yourselfer to build a dormer about 6 feet wide and 9 feet high, with one window.