I don't see any pictures. 1 panel of egg crate should suffice if im imagining what you want to do correctly. You can use pvc pipe to elevate the false floor or Just use extra egg crate pieces. A lot of people use screen for the drainage layer but if i built another one i would use filter fabric as i found the water got tainted quickly and never recovered... But i had a water fall feature in mine.
Don't forget to buy lots of zip ties to fasten the egg crate pieces!