Adirondack Chair

I would like to build the world's largest Adirondack Chair. 3 times this size and 16' wide seat slats. https://hahabird.com/blogs/projects/the-big-chair-building-your-own I need a set of engineered plans for this project to submit to the state of California for a building permit. I would like to use wood harvested from the property where the chair will be build. So no grade stamp on the wood.