flood and drain setup any ideas?

So in my first grow now but thinking I want a flood and drain system im trying to figure out how to build it is proving difficult seeing as im new to this concept so I have a 20gal black tote which is where I want my roots to be would have this six inches off the ground where below it I have the drain water catch so if draining below at a constant rate would I need a pump filling at a constant rate? I imagine you dont want to let the roots just freefall in the air(from 6'' verm an per mesh pot) or is them hanging in the air not ad for them

https://www.rollitup.org/t/dadios-flood-and-drain-closet.372572/
Here is a link to my grow op . I built my own Flood and Drain system using Rockwool. It is a basic set up that can easily be modified and changed to suit your personal needs.