I made mine following a video that someone posted here from a nursery that is actually local to me.
Essentially I make 3 rectangular frames from whatever materials I have. In this case, it was 2x8s. I stack them, then use 2x4s to secure them in the corners and middle. These are laid on top of thick weed barrier. I also laid down thick cardboard inside...
Because next you line the inside of the bed with visqueen or pool liner, whatever you have. I used 6 mil plastic sheeting from Lowe's.
Line the bottom with 8 - 12" of river rock. I used large, smooth 4" rock. Picked up a cubic yard from the local landscaping company for $50 which allowed me to fill nearly (3) 10 ft x 2 ft beds. Add 4"drain tile so you can add water as needed directly below the soil. Added in an overflow pipe in case we get too much water or rain.
Here's a picture at this point -
View attachment 3796498
Then I put down a thin weed barrier, mostly to keep the soil from getting into the pipes below and clogging them. Then, simply add the soil to the top. In my beds, I have 8" of rock to act as the reservoir to 16" of soil above. I left the 2x4s extended above the bed as supports so I can cover with shade cloth or insect netting, as needed.
Here's the final product -
View attachment 3796506
I have thought about adding a layer of wood logs or mulch between the rocks and soil but I haven't gotten around to trying it yet.
FWIW, I have hugelkultur beds too. I really like them too... I use them for my flowers and shallow root veggies. I chose to create the self-watering beds above for my potatoes, carrots, and tomatoes, mostly...
