In contrast, the incidence proportion can be calculated as 16 â 2,100 = 7.6 cases per 1,000 population during the four-year period, or an average of 1.9 cases per 1,000 per year (7.6 divided by 4 years).
The Costs. Minimum Cost: Approximately $.50 per square foot. Maximum Cost: Approximately $2 per square foot. The size of roofs vary immensely from a standard, urban roof measuring about 800-square-feet to suburban roofs, which often range above 1,500-square-feet.aximum Cost: Approximately $2 per square foot. The size of roofs vary immensely from a standard, urban roof measuring about 800-square-feet to suburban roofs, which often range above 1,500-square-feet.
HomeAdvisor's Cost Guide says the average national price of a roof installation for most Americans ranges from $5,913 to $7,853. At the high end, people pay as much as $12,000; at the low end, they may pay as little as $3,000.