After we bought our house, we started looking into ways of removing the copious amounts of gravel covering portions of the yard. When we started figuring how much a truck load of gravel weighs, how much time (and work!) is involved to shovel it out by the wheelbarrow load, and the associated dump fees, we decided to work with the rock. Raised beds were the best option we were able to come up with to reclaim functional gardening space.
We could have never afforded to build these had we not found used cedar 2x6's that the parks service was throwing out and redwood 2x6's salvaged from a deconstructed deck. Those two windfalls yielded enough good rot-resistant wood to work with.
Additionally, I added a soaker-hose irrigation system built into the planters with quick-connect fittings for easy watering.
You will need cedar, redwood, or similar rot-resistant wood. Some people use pressure treated wood, since the new types don't contain arsenic, but some people are still wary. Cedar lasts longer anyhow, and I think it looks good. New, it's really expensive, but look for old decks, playsets, pergolas, etc. that you can haul for free.
Use a good coated, rust resistant screw to assemble. I used 3" coated deck screws. Each layer is assembled with 3" galvanized nails.
6 -- 2"x6"x7'
6 -- 2"x6"x3'
2 -- 2"x6"x7' 10" mitered 45 degrees toward center on each side
2 -- 2"x6"x3' 10 1/2" mitered 45 degrees toward center on each side
8 -- 2"x6"x 16 1/2" for corners
Circular saw or crosscut hand saw
Strong drill or screw gun, preferably corded
Step 2: Cut Your Boards to Length
Make all your cuts. Make piles of each size piece. Mark-up and cut your miters. See previous slide for cut list.
Step 3: Assemble the 4-sides of Each Layer
You are essentially making 3 boxes that stack on top of each other. The boxes are attached to each other by two-piece corner bracing. All the simplistic construction is covered by a nice railing along the top that makes everything look nice and protects the joints from the majority of rainfall.
Step 4: Attach the Top Rails
Now, attach the top rails (the mitered pieces) with the shortest side facing in. I recommend assembling piece by piece, clockwise or counterclockwise around the box in case you need to trim the final side. Depending on how straight your boards are, you might not have to trim them any.
Step 5: Install Soaker Hose
When you buy a length of soaker hose at the hardware store, it's usually sold in 50' sections--- way more than is needed for a single box. Cut off enough hose to go down and back, long ways across your box. Then, install a male barbed garden hose fitting, and secure in place with a hose clamp. Then, cap off this threaded male hose fitting so the water is forced through the pores in the hose, not out the end. Finish by attaching a quick release coupler on the outlet of the hose, so you don't have to fumble with screwing a hose in every time you water.