How much to you think it would take to build a table. ? And the roots are openly exposed to light in the tray? Do you have an overhead pic of one of your tables?
I have tried and failed
dismally to DIY some flood trays, thinking it would save some dough. I've built frames of 2x4 timbers with a plywood floor and lined it with plastic, put plumbing fittings in one corner and blocked it up so water drained to the corner. Problem is the plastic tends to pinhole with use, moving pots around and whatnot. Leaks and wood construction don't mix well, neither do leaks and non-resilient floors/coverings.
I use commercially available vacuformed plastic trays, 900mm x 900mm. They are on stands made from ~25mm square aluminium (never steel) tubing, fitted together with Qubelok plastic connectors.
The tubing & Qubeloks are available at Ye Olde Gargantuan Hardewarre Shoppe. Trays come from most any hydro supplier. The commercially made plastic tray is simply the best tool for the job, but even good ones eventually crack. Keep a tube of silicone sealant handy.
edit: Most trays are sold without holes for fill & drain fittings drilled. I USED to use a hole saw and a drill to make these openings. I now use a homemade hot knife (a 60W soldering iron with the tip pounded flat) to melt the holes, clean them up with a bit of sandpaper on a dowel rod. Prevents future cracking around the holes.