Using the information you have provided and not visually inspecting the roof, the black spots on your roof are more than likely algae. Most shingle manufacturers use copper or zinc coated granules to aid against the growth of algae.
Two-stroke oil (also referred to as two-cycle oil, 2-cycle oil, 2T oil, 2-stroke oil or petroil) is a special type of motor oil intended for use in crankcase compression two-stroke engines.omparing regular lubricating oil with two-stroke oil, the relevant difference is that two-stroke oil must have a much lower ash content. This is required to minimize deposits that tend to form if ash is present in the oil which is burned in the engine's combustion chamber.
In the UK when I was younger, a lot younger there was a lot of motorcycles and a few cars such as Saab fitted with two stoke engines, at that time petrol stations had a separate pump which could be set to the selected petrol-oil mix ratio for the oil to added to the petrol while it was pumped into your petrol tank.wo stroke petrol is petrol mixed with oil, it has to be mixed at the correct ratio, if you buy your own two stroke oil, I'm sure some garages sel it.