Anyone use something like this for roof cleaning?
Size of the roof (area) is only 1 of about 7 major costing factors. The material cost for the mix (SH+Surfactant) is the only thing directly impacted by sq ft and it's only about 10% of my price. I can eyeball (estimate) the size (how much roof wash mix) from a bing birdseye view just based on the size of known objects in the image (cars, doors, streets, sidewalks, etc).
We've been estimating all roof cleans and house washes from aerial view for two plus years now. For me this would be waste of money and time. I'm usually not off by more than 10% on costs and time (over/under) at the curb as it is.
For someone new at roof cleaning, this might give them some comfort in pricing a job. Over time, you'll start seeing the same basic floor plans over and over and eventually, you'll be able to spit out a price and have an idea of gallons within just a few seconds of looking at a roof.
As an example, and a caution to anyone pricing "only" by sq ft, The pricing factors of cleaning half of roof with 2500 sq ft is not half of the price of cleaning the entire roof. The travel costs, mobilization, demobilization are the same for 1250 sq ft as for 2500 sq ft. You save ladder movements and material but since the ladder is already off the truck it's not a doubling of labor to double ladder moves. Other costing factors that will eventually get you if you cost by the foot are dormers, pitch, height, access, vegetation, downspout discharge, and terrain slope. Also, usually, the half they want cleaned is the worst side, so you are spending almost the same time for half the price.
I used a half roof in that example but the points hold true on any "area" pricing model.