In Washington state, covered marinas have to have aluminum roofing, which will melt and vent the fire. They also have to have a vent at the peak of the roof. My marina (La Conner) has an open peak made by raising one side of the roof above the other creating a long slot.
Everett Marina had a boat fire in 06-07, which melted the roof over 4 slips, and contained the fire to 4 to 6 boats. The live-aboards were told by the marina, that in case of fire, to untie any NOT burning boats in way of the fire. Then push the not burning boats out of the slips, creating a fire break. And they were told to NOT untie any burning boat, as the fire fighters cannot reach a floating, burning boat, and it could drift into other boats and spread the fire. The Everett Marina is in a closed basin, with only one entrance. Any drifting boats could be rounded up later.