Well- flooding a 4x8 requires a HUGE res-100-120gal- expensive in terms of nutes, just so you know.
You'd need like 4-500 liters of hydroton to fill it as a bed- I'd do smaller containers full of hydroton to cut that expense, not to mention being able to re-arrange the plants if needed. Standard nursery pots work fine.
You can space the smaller containers w/ " blanks"- 2 liter soda bottles work well, as they displace volume w/in the tray. Fill em w/ h20 so they don't float. Reduces minimum res volume- but adds dead weight to the table ( think about how much a flooded 4x8 weighs). Put em on their side if it'll better match your flood profile- you don't need a level in the bottles any higher than max flood, that's just extra weight. Or any mechanism to displace volume w/in tray that appeals to you will work. Plastic's a good idea- I wouldn't use cinderblocks, f'rinstance...

For that size table, RW slab works well, drip or flood. Lower max flood level=smaller res/nute$.

How much biomass feeding off res @ end of cycle? If yer growing trees, math changes...

You can also do a bunch of, say, 2-3 gal polypots w/ constant drip from 1/4" tube- use a couple of feeds per cell, in case you lose one. Again, more complicated, but smaller res/lower nute$.

Cost/benefit equation- depends on yer nute cost, how often you change res, etc.