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.