Here is a tutorial on a galvanized raised bed we made. By using galvanized roofing material as the structure it will last much longer versus using wood.
*Note: These measurements work for us. You would have to calculate your own measurements.
Total supply cost: $70, but it could be cheaper if you use different wood/supplies. We went with cedar and galvanized screws so we can ensure this will last us a very long time!
Total Time: 1 day
Yield: 4 ft by 8 ft