If you want to build a trellis, it is important to make good decisions ahead of time. Building a trellis is a relatively straightforward project that a novice gardener should have no trouble with, but it is possible to make bad decisions at the planning stages that ruins the project. It is most important to choose the correct type of trellis, as not all types are ideal for all situations. Additionally, when making this choice, it is important to consider the type of plant that will be climbing the trellis, as different plants function best in different situations. What follows should give you enough information to get started making your decision.
Generally speaking, when people hear the word "trellis," the image that springs to mind is this particular type. It is not hard to see why—the flat trellis is quite widely used, and for good reason. The flat trellis refers to any type of trellis that is flat and supported by leaning against something, such as the wall of a house or a fence. This type of trellis has a functional purpose, but it can also be used as a decoration on its own, or as a separating wall between 2 areas.
While you could buy a pre-made flat trellis, there is nothing stopping you from building your own. If you want to do this, simply purchase a section of lattice fence, and some 2x4s. Plan out your trellis carefully, figuring out what size it should be ahead of time, then measuring and cutting your section of lattice fence to this size. Once you have done this, measure your 2x4s to make an appropriately sized frame. Once you cut them and attach them, you will have a sturdy trellis that is ready to be set up. Use it with coral vine, ivy, or any other climbing vine.
The obelisk is another type of trellis that can be used for many different kinds of plants. While it can come in many shapes and sizes, the basic form of this variety of trellis is a pyramid. However, the height, width, and number of sides can vary dramatically. There are many pre-built commercial models of this type of trellis, but there is no reason you cannot build your own.
In order to make an obelisk trellis, you will need 4 2x2 boards roughly 8 feet in length, and 4 1x3 boards roughly 4 feet in length. While exact sizes are not important, having the boards be equally long is.
By screwing the 2x2 boards together in 2 V shapes, then screwing the 1x3 boards onto the V shapes as if they were steps in a ladder, you can have the basic structure completed before you know it. If you have done this, all you need to do now is set up your obelisk trellis by leaning the two halves together, securing it with twine and stakes in the ground if necessary. Set up your obelisk trellis over squash, runner beans, tomatoes, or any plant that likes to climb.