Wood is a renewable and a carbon trap. On site, dirt is a good choice for a building material. You can also use it to bulk mass. You just need a digger and some grunt work. See building with rammed earth.

I've a friend who has just added to his 17th century thatched cottage with like materials: oak timber frame, timber cladding and wattle and daub, which is dirt and wood/hay/hair. It's lovely and solid. Sadly planning officials insisted on an over the top concrete foundation that negated all his hard work with his sympathetic build.

The wood is good!