Garden trellises are a must for some plants. If you grow anything with vines, unless it is near a chain link fence, you will need something vertical for the plant to attach to. Store-bought trellises can be expensive, and will not always come in the style that you want for your garden. Building one yourself is not very difficult, requires no special skills, and is usually a lot less expensive than what you will find in stores. The main things to consider are the weight of the plants your trellis will support, and the longevity of any building materials you use.
Take measurements of the area in which you wish to place your trellis. Write these measurements down. If the plants you will have climbing your trellis love sun, observe how the sun hits that area as it moves through the sky during the day. Most trellises should be at least 4-feet tall in order to take full advantage of sun exposure for your plants.
Consider simple and practical trellis designs that are also attractive. Think about an equidistant criss-cross trellis reminiscent of a tic-tac-toe board, or a fan-shaped trellis with cross-pieces. Both are beautiful on their own, and will be even more beautiful when your plants are growing on them.
Draw your ideal trellis design on a piece of paper. Use a ruler to ensure straight lines, and write suggested measurements next to each piece as well.
Remeasure according to the design you have drawn in order to spot any potential problems before you begin work.
Consider building materials for your trellis. Wood will work, but remember that it needs to stand up to the forces of the elements, so you may consider treated wood. Cedar and redwood are naturally rot-resistant, but can be very pricey. Bamboo canes are a good option, as they are strong, lightweight, and resist rot naturally for 8 to 10 years. They are also an inexpensive renewable resource. Metal can be lovely, but some metals can rust. Metal may also be difficult to work with unless you have previous experience.
Consider hardware and/or fastening methods for your trellis. Wood should be secured with galvanized screws. Metal may be secured with galvanized screws, or welded together if you have the knowledge and tools to do so. Bamboo can be lashed together with twine or lashing cord. All methods of fastening need to be weather-resistant.
Stand in your garden in front of the place where you will put your finished trellis. Visualize the finished work with your current garden design scheme to spot any problem areas before you start. Adjust your design as necessary.