They're normally built from a mixture of natural materials with timber/metal thrown into the mix. Hi sense of style when it comes to Halloween is superb. He's inspired so many people down the years who have all tried to copy his work but don't quite get there. Very, very well done. I recommend looking at his past yard haunts on youtube.
I follow him on online as he has a side blog which he updates regularly.
When I first started visiting various Halloween forums online I got told the backstory of how this chap got into making this style of work. He entered a scarecrow making contest that gets held every year at some small town. As you can see all pretty bog standard stuff. In fact here's a link to his video of it.
Suffice to say the judges didn't know what to make of his entry which stood out a mile! He got nothing but shocked stares. It was from then on his style of art really took off.