More and more people are using raised beds in their gardens. The main advantage is you can completely control the quality of the soil you have to work with. It is suggested you till the existing ground before you build a raised bed to allow the old and new soil to work together.
It’s best to have a bed at least 6″ tall to allow a sufficient amount of soil, but many people prefer raised beds that are 16″ to 20″ high so that you can sit on the edge of the bed while working with your plants. Be sure to allow for adequate drainage in a raised bed.