Step 1: Collect It.
It's relatively simple, figure out what dimensions you need, this will probably be determined by what garden mesh/wood you have on hand. Mine is 3' x 6'
Wood boards of the right lengths
Wood glue (optional)
Garden Mesh of the right dimensions
If you have a corner clamp...get it.
Step 2: Cut It.
Set your miter saw to 45 degrees and cut an angle into each board. Make sure that you make the cut off the same side of each piece. You should be turning each plank into a trapezoid. If you're afraid you may make a mistake, draw cut lines and line them all up to make sure they will fit into a rectangle. Make the cuts as close to the end as you can, so that you have some nice little triangles to use later.
Step 3: Screw It.
This is the hardest step. Use the glue to add some rigidity, and then use a screw to make right angles. The best way that I've found to do it (because the angles cause them to slip) is prop them up in the grass. When they start to dig into the dirt, they stay in place. Once you have a rectangle, use four of your little triangles as gussets to reinforce the whole thing. I used two screws per triangle and some wood glue. By now, you should have a nice strong frame!
Step 4: Mesh It.
From here on out, it's smooth sailing. Just lay out your mesh over the frame and use the zip ties to attach it. The tighter, the better. Trim the mesh if it needs to be trimmed and you're ready to set up!
Step 5: Use It.
Luckily, I have something to lean my trellis on. If you don't, either cut another piece of wood to hold it up, or hang it on something. If your plant needs a trellis, it probably has little tentacles coming out all over looking for things to latch on to. They look like curly strings hanging around. All you need to do is guide a few of these strings onto your new trellis and they'll figure out the rest. It's been a couple weeks since I made this, you can see the difference yourself: