Steps:
- Cut a piece of 8-inch-wide aluminum flashing to length using aviation snips; you could also slice through it with a sharp utility knife.
- Measure for the leading edge of the flashing to determine how far it’ll hang down in front of the window trim.
- Use a metal brake or homemade bending brake to bend the leading edge of the flashing passed 90 degrees.
- Make a gauge block from scrap wood to represent the thickness of the window casing and trim.
- Slide the flashing into the brake, using the gauge block to position it at the proper depth.
- Bend the flashing to create the wide flange that extends up the wall.
- If using a homemade bending jig, set the 2x4 tapping block on top of the bent flashing and strike hit it with a hammer before removing it from the jig.