Measure the Area and Mark it Out
Roll out a tape measure to the desired length and sprinkle flour over it. Do this for all sides so you can see what it will look like in the landscape and make any adjustments you like. Although most raised beds are rectangular, they can be any size or shape you like. You should be able to access all the plants in it, though, so keep that in mind when you choose the location and the dimensions. Make sure that the area will receive enough sun exposure for the plants you plan to include.