Using a Tip 5 (or any small round tip) hold the bag at an angle against the eaves of the roof.
Squeeze, moving the bag and tip in an up and down motion as you trace the eaves and edges of the roof.
To end a section, stop pressure and pull tip away.
The pressure on your bag determines the thickness of the line. Squeezing lightly will create thin zigzags and squeezing heavily will create thick zigzags.
For even zigzags, try to keep steady pressure throughout piping. For zigzags with tapered ends, use a lighter pressure to start, increase pressure as you move down towards the middle, and decrease pressure as you move up to end the section.
The movement of your arm determines the height of the waves and the distance between them. A tight up and down motion will create tight zigzags, and a relaxed motion will create a loose zig zag.