FREE 15L Bike Pannier Sewing Guide
Suggested donation of £2 (or more) if you want to help support more free patterns, but you can have it for free if you prefer :)
Pattern has markings for adding a webbing ladder to use with straps to attach to your bike, but feel free to use hooks or whatever.
Making a internal pocket for stiff plastic on the back panel is highly recommended.
Download includes a large format A1 file, and A4 + US letter tiled pdfs