4x4 corners are ceder. Shelves are (2) layers of MDF 1/2" and 3/4" glued together with 1/4" oak plywood also glued together. End caps are 1/4" real oak. I notched out the 4x4's for the shelves. Copper deck caps were my idea, but it could be built with the top shelf covering the tops of the 4x4's. I based the shelf spacing based on my equipment and made the bottom shelf high enough for lp's. I bolted it together with brass 3" screwws and added vertical bracing in the back to hide wires and add some stability.
Stunning job on your equip. rack. I too just built my own but after seeing the robustness of your build you have me rethinking mine all over again. Could you provide me with some more info on it (species, final dimensions, joinery etc.)? Congrats on an awesome rig.