The best part is if the plastic wears out or gets a leak in it, it's easy and cheap to replace. I think when I was building this I priced channels that were made of PVC and similar dimensions, but they wanted like over 100 bucks per channel. I made 6 of them this way and only spent like 50 bucks on plastic, silicone and staples. Already had the plywood on hand as I said.. My channels are approximately 8 feet long (the length of a sheet of plywood) about 8 inches deep and 8 inches wide and will hold 6 plants each.. If taken care of properly, should last me the rest of my life.
Oh, and I found a plastic tote made to store fake Christmas trees at Walmart during the holiday season as a reservoir. I just lined the outside of it with panda plastic as it's a clear tote. Works great as a reservoir. It's not too tall, nice and wide so all the channels can just gravity drain directly into the res. Holds about 50-60 gallons or so.