I've built things with PVC before, and it's pretty flimsy. I wouldn't recommend a plant stand made out of it, once you factor in the weight of the water. If you do use it... reinforce, reinforce, reinforce!

I use this one every year for seedlings. Easy as pie to make, assemble, tear back down and store until needed again by simple labeling. (I did make some adjustments by making the side pipes longer for taller plants and raising the lights as they grew)

Here is a link that might be useful: PVC Plant Stand