How to Build12×20 Barn (Gambrel) Shed – Shed Plans John Greene 8 years ago 0 Min Readshare12×20 Barn (Gambrel) Shed with Metal Roof, 8′ Double Barn Style Doors, Windows, 8′ Treated Ramp and loft.Now You Can Build ANY Shed In A Weekend Even If You’ve Zero Woodworking Experience!Start building amazing sheds the easier way with a collection of 12,000 shed plans!source