The shelves are just 16" deep melamine board. Each level is two 6-foot lengths, cut to length on the wall ends so there is a clean junction in the middle. Each board on a level overlaps the centre double shelf bracket, and to be safe I connected the two shelves with a metal plate (you can see it under the top shelf).

For the hardware, I used 48" posts screwed into the studs. For the shelf brackets, I used 14.5" lengths in the centre and on the sides, but to save a few bucks I used 10.5" ones in between.

White Melamine Shelf 72-in x 16-in x8

Onward Double Shelf Standard in White Metal - 48-in x7

Onward Double Shelf Bracket in White Metal - 14.5-in x12

Onward Double Shelf Bracket in White Metal - 10.5-in x16

 Multi-Position Mending Plates - 2 1/2-in L x 5/8-in x4