Since you are starting from scratch, please consider this post by Ryan of V1 Engineering, showing an affordable and doable way to get a full size table, without needing to resort to use of Unistrut metal rails: ~ $200 Full sized Lowrider table, Non-CNC Build
If you are wanting a torsion box design like that, I’m pretty sure Ryan @vicious1 shared the CAD file for what he did: quote from his post:
CAD - Onshape
Does that work for you?