These can be built from any material that is at hand.
The depth of the soil is determined at the time of building. My drawing is 12 inches.
The general rule of thumb for garden width is to measure from your armpit to your wrist. That measurement should equal one half of the garden width.
BUILDING IN WOOD
I have specifically left out the sheathing in order to show construction detail. Use either ½” CDX or Luan underlayment. There will be about 1 foot of offal left over. Use the waste to produce gussets that will be fastened over the plate joins.
The Bill of Materials is for cost estimating only. Start by building the octagon plates first, then build from there using the plans only as a construction guide. Your dimensions, once you start to build, will be different; I guarantee it.
Fixtures make your life much easier. Build your saw guides with care.
If you have never used a hand held circular saw before, get some training. I once had a building trades student graduate, get a job, and immediately violate one of the basic safety rules. He wound up disemboweling himself. He survived, barely. BE SAFE PEOPLE!
Below please find the drawings. If anyone has access to CAD software, I would be pleased to ship you the DXF file. megiddo at prodigy dot com