We built some beds about 8 years ago out of thin cedar boards, but because they are very thin, it is hard to screw them together. We ended up having to put metal bracing on the corners. The boards haven't rotted, but the screws keep pulling out of the thin boards.
Recently, here at permies, I have read that cedar is allelopathic, and not really that good for garden beds. Mine have not been very productive, but whether that is because of our dry climate, or the cedar, or the nearby tree roots invading the soil in the beds is not clear.
I really prefer to use 2x6 or larger boards (like 2x8 or 2x10) to give a deeper bed, and one that I can kneel or sit on the edge while working in the bed. Yes, they do rot out sooner, but they still last a number of years. And if you decide to move, you can unscrew the boards and take them with you if not going too far.
I also like to screw 1 foot long pieces of white pvc pipe--1 1/2 inches diameter, to the bed frame, (with pieces of plumber's metal strips--not sure what the name is) so I can add hoops (made from black pvc pipe) and cover them with tunnels to extend the harvest season. Then I can start planting a few weeks earlier, and keep things growing a few weeks longer in the fall. Or even put up a shade cloth in the heat of the summer. In a heavy snow area I find the hoops hold up better if I get my son to bend pieces of
rebar to slide inside the pipe to give it more support.
I have used these tunnel-covered frames in downeast Maine, and in New Mexico at 6000 ft elevation, and now here in CO, to give me an extended harvest of cold-tolerant crops. In a cold climate, I do prefer to install the white pvac foundation pipes on the outside of the bed, so I can lay another cover, made from 2x2s and plastic or rigid
greenhouse glazing, to give even more insulation. in NM I was able to harvest greens all winter, even when there was snow on the ground.