Forget straight lines for a moment and think outside the ubiquitous square box. Rebar is flexible and can easily be bent to make arches, tunnels, domes, and free-form curvy shapes. There is really only one step in making a rebar trellis; putting the rebar where you want it and tying it in place with wire. There are several design considerations however. This instructable will cover the simple "how-to" and the more complex "why" of design considerations.
A rebar trellis can also be converted into a cement structure by covering it with a mesh material and then plastering it with cement. My home was made using a trellis-like support for nylon fishnet and cement. A second-generation trellis now covers my home for shade. It could also be cemented someday, allowing for a third-generation trellis over that, and so on. The end result would evolve into something resembling a termite nest-like city, and create a radically different way of life for everybody involved.