I'm planning to do the same (without creating too much of an eyesore for me and my neighbors). So great to see him documenting this.
One thing his construction will run into though is his wooden pillars rotting quickly. Always keep a healthy distance between wood or it will be soaked quickly.
I'd say this is why they have the treated posts resting on gravel with concrete filling the remainder. This would stop water pooling, and if the concrete was mounded a little bit, keep more water away from the posts.
He says they're "treated", which I think means "impregnated with alkaline copper quaternary or similar poisons". So I think it might survive a good while even if it stays wet after it rains.
One thing his construction will run into though is his wooden pillars rotting quickly. Always keep a healthy distance between wood or it will be soaked quickly.