Tomato cages always seem to be too small, too flimsy and simply, not enough for the indeterminate tomato plants I grow. This year I decided to make a 3-D PVC grid to support my tomato plants. My final cost was about $55. The tomato portion of my garden is roughly 6'X7'. Since your garden will probably have different dimensions, your cuts will be different lengths than mine.
Step 1: What you will need
For my garden, I needed
---21-10' pieces of 1/2" PVC pipe
---8 -X shaped PVC connectors for 1/2" PVC
---38 -T shaped PVC connectors for 1/2" PVC
---a tape measure
---a marker, such as a sharpie
---an electric saw of some sort (I used a miter saw)
Step 2: Cutting Tips
Measure the PVC using the tape measure and mark it with the sharpie. PVC tends to break easily when cut with an electric saw. To prevent this, wrap the area to be cut with duct tape and re-draw the line on the the tape. The duct tape can be removed after the cuts are made. The length of the cuts for my garden will probably be different from your garden, but I will list them in the following steps so that they can be used for reference.
Step 3: The first cuts
I started with the 4 corner pieces and 4 center support pieces and decided that 10 inches into the ground would be enough to keep the grid stable. I wanted each level of the grid to be 20" above the next, so I made my first 8 cuts at 30" each and pounded each 10 inches into the ground (I drew a line 10" in so that I could be sure to push each piece the same distance into the ground. The four corner pieces each should have a T-shaped connector bracket on top. The four center pieces should each have an X-shaped connector bracket on top.