Flashing an Octagon Window on a wall with external insulation – GreenBuildingAdvisor

Does anyone have some details on flashing for an operable Octagon window, we are replacing the old lap siding.

I am in Zone 3 warm humid.

Updated Wall assembly from inside to out:

1/2″ sheetrock, R23 fiberglass insulation in 2×6 studs at 24″ on center, 7/16″ Zip sheathing w zip taped, 1″ polyiso, 1×4 rain screen, Lap cement siding.

What are the head flashing details, I will use Zip stretch tap and flashing tape for rough opening &  5 degree sill for drainage.