If you use self tapping screws you won't need to drill a hole. Just put the right
bit in your drill motor and drive the screws right into the wood. I just showed that bit so you can see what I mean. Those roofing screws are hex headed and you drive them with a bit like that. Your local hardware store will sell them individually so you can get one the right size. They are often 5/16" but not always.
I'd mark the screw hole locations. Start the screws--drive them in maybe a 1/4 inch and remove the screws. Coat the bottom of the cleat with Dicor, position it over the holes and then drive the screws all the way in. That should seal the cleat.
The reason for doing it this way is that the cleat may be hard to control, that is will be slippery, with the sealant on it. So pre-drilling the hole part way prevents that from being a problem. The screw inserted into the hole will control the location of the cleat. Not putting the screw all the way in gives you the tightest possible fit in the hole it creates. Do not over drive the screws that will ream out the hole and give you a poor fit.
Thinking about it I would use 1 inch long screws max, since I don't know how thick that roof is. Using these roofing screws you won't have to worry about them corroding. They are coated and designed to exposed to weather. Stainless screws are weaker and you have to worry about wringing the head off the screw when you drive them.
