I just got a 80 sq ft plot at a community garden. The beds are raised about a foot. I have been toying with the idea of digging one foot below the surrounding area in my plot so the bed is then 2 feet deep. I thought I'd try to get a bunch of one-foot logs and stack them side-by-side vertically so I'd have a one-foot deep bed of logs. I could fill them in with wood chips, etc. Then spread a bunch of chopped up fungi on top to help inoculate them. Finally, I'd replace the one-foot deep soil that had been there originally.
In a couple of years, it should be a good producer for a number of years afterward.
But is all that work worth a one-foot deep hugel? We're having a drought in California. I think it might be a great idea for me.