I found another great way to build gable and vaulted roofs — with pallets: Pallet Pavilions
The site referenced above shows how pallets can be used for walls and roofs. This is exciting because free pallets are usually quite easy to get in most countries and they’re very strong. Many are made of hardwood such as oak.
I’m most excited about using pallets for roofs because this is one of the most expensive parts of a structure. Using pallets opens up a lot of possibilities for affordable roofs: medium-sized vaults (which are difficult to build with earthbags larger than 8′ wide or so), corbelled roofs for roundhouses, cathedral ceilings and more, as well as curved, free-form shaped houses shown above.
You can even use pallets to make gabled roofs. Cut pallets into 16” sections, stack them flat, corbel each course a few inches and nail together with a nail gun to create a conventional looking gable roof. Once covered with metal roofing, framed on the ends and trimmed out, no one could tell how it was built. This technique is limited to small spans and areas without building codes, but it is another dirt cheap building technique for building almost for free.