If it's a big honking space sprinkler
Thats the wrong idea
You run a very big soaker hose along the top of the roof
EXACTLY! A pipe along the ridge of the home, perhaps built in for cosmetic appearance. In a fire, the pipe runs water along the ridge lines of the roof, and water POURS ("not "sprays") over the roof's surface, completely covering the roof with a sheet of water. Now that water reaches the edges of the roof, and the gutters are designed to channel the water straight down along the wall's surface to the ground. The water then falls into channels that return it to the cistern for reapplication. The entire home is continually covered by a SHEET of water, for as long as the fire is a threat. WHY is that so hard for people to understand?