The one odd “H block” shown in the video is a tricky to find item, but appears to be a:
Oldcastle 8-in x 8-in x 16-in Gray H-Fence Block
Item #: 102097 (Lowes Item#)
I could not find any at my local Home Depot, but a Google search showed this POSSIBLY available at Lowes.
The Savannah Arsenal Project 