Cost driver considerations: building access, height, building region, total square feet of project, type and quantity of roof curbs and flashing details, roof tie in details, drainage details, roof insulation and coverboard options, tapered insulation requirements. Is it a tear off, roof over or skin of roof. Using a reputable contractor, etc. There are many factors to consider and cost can range from $4.50 to $10.00+ per square foot.