In order to design a planter box that is appropriate for the space or location you have in mind, you need to be very familiar with that particular location. Is it a window, deck or porch? Depending on your desired location, the attachment method may vary, which should be considered when designing your planter box. Will your planter be shielded from the elements? Depending on the location of your planter box and the conditions of the location, the materials used to create your planter box could vary.
Another key to designing a planter box is knowing the materials you will be using in the construction of your planter box. Wood can effectively be used by most any planter box designer, no matter the skill level. Wood is an excellent choice of material to plan your designs around because it can be cut, shaped and sanded into a variety of designs depending on the skill level of the builder. While high density poly ethylene plastics, terra-cotta, glazed clay, stone and wrought iron are also materials used in many planter box designs, you should keep in mind that these materials can be difficult to work with if you aren't experienced in handling them.
A final way to get the planter you want is to draw up detailed plans with the aesthetics and accurate measurements of the planter box. The quality of the final product will depend on your planning. One way to help with effective planning and execution is doing the proper research on designing a planter box, which may include watching instructional videos.