Very quick and easy project. Used the plans but adjusted the width and used pocket hole screws. We made ours 54" wide. After building the entire box and horizontal shelves with pocket holes you can secure the vertical pieces with brad nails. Start with the top row first and you can secure all of those with brad nails. Then use pocket holes on the top of the bottom vertical pieces because it won't really show. You won't be able to nail it since the top vertical piece will be in the way.
I put some extra 1x2 scrap pieces on the bottom of the shelves for extra support but it would probably be fine without it. We just knew we were going to be loading this thing up and wanted it to last forever and it's not visible anyways.