You will notice some similarities between my build process of others but I hope to point out a few things that might help you in your build.
Additional pictures of the project and reference material can be found at http://coknown.com/project/1338
Step 1: Materials list
Its a good idea to draw out your plan with relatively accurate measurements and even better if you can stake it out at the site to get a solid sense of what its going to look like when its done.
The basics are wood, rock, PVC pipe (or some other water delivery pipe), landscape fabric, heavy duty plastic and soil.
I used cedar to build our beds as I wanted them to last, cedar matches the cedar fence close by, and I didn't want any leeching into the soil from pressure treated products. I've read, by not confirmed, that if the bed is completely lined in plastic then there shouldn't be any leaching of the pressure treated product into the soil. Makes sense I suppose but I still didn't want to go that route even though it is cheaper to use PTP as opposed to cedar.
Step 2: Select a flat area
Luckily for me, the area I picked only had a slight grade and by using a line level it only took a small amount of digging and redistribution of dirt & rock to get the area level.
If you have staked out your beds and know their location, by using a line level you'll have a very good idea of how much dirt you'll have to move to get a flat area.
Step 3: Build & assemble beds
Depending on the size & shape of your beds, you'll have to determine the best way to make them structurally sound. Two of mine are 12 feet x 4 feet and one is 8 feet x 4 feet. All 3 are 15 inches deep. Keep in mind that soil will wick water up approximately 1 foot. Consequently, you want to account for how much soil you need for the kinds of plants you want to grow vs how much the soil will wick water.
A word about the rock. For the first layer, I used round pebbles (landscape rock) from a local big box store. The second layer of rock I used was volcanic rock to fill up the 3.5 inches I wanted for my water reservoir (covers the 3 inch PVC pipe). You don't want to put volcanic rock on your heavy duty plastic as it might puncture your plastic and destroy your reservoir.
As for drilling the PVC, whatever large bore bit you have, use that and stagger holes along the side and bottom of the pipe every 6 inches or so. You'll also want to cap the end of the pipe so all the water you pour in doesn't rush out the end as opposed to being evenly distributed. I didn't use a PVC cap but instead stuffed old (but clean) rags into the ends of the PVC pipe so the cloth would allow the water to leak slowly.
Step 4: Soil, trim & ready to plant
Once you've filled your beds with soil, trim away the excess plastic and you're ready to plant.
Again, I have many more pictures and other reference pages available http://coknown.com/project/1338
I'd also be happy to answer any specific questions about this project.
Thanks for reading through this.
Next up will be my water harvesting system.