Leftover roofing shingles can be used as siding for a storage or garden shed. You will want to follow the appropriate installation process for best results. This page gives some advice about using roofing shingles to side a shed.
Using Roofing Shingles to Side a Shed?
Home Remedies for Shingles
Is Vinegar Harmful to Septic Tanks?
Ice Maker Arm is Stuck
Cleaning Black Streaks (Mold) on a Roof
Shingles Advice?