We built three 4x12 beds that are 8 inches deep. We built them in my "workshop" (aka garage) on the floor and had really high tech equipment such as a large outdoor garbage can and hand saw to cut the 2x4 corner stabilizers. All joking aside it took a little bit of time but was a easy project.
I bought eight 1x8x12 untreated cedar boards, two of which were cut to 4 foot lengths for the edges. Luckily the man at the lumber store was feeling nice and since we only had 4 cuts did this for us. We also bought a 2x4 to make the corner supports. We cut the 2x4 into eight inch lengths since we bought 1x8 boards only to find that a 1x8 is technically really .75x7.5, whoops. The extra half inch on our corner supports will be used the anchor the beds in the ground, so it worked out.
I'd also like for you to notice that on March 30th when it should be in the fifties it was in the high 30s and snowing as we were building our raised beds. It just felt off to be getting ready for gardening as it snows.