Keep in mind that the shelves are not adjustable and some larger helmets will not fit, like the Rubies Supreme Vader. But a good value for an outstanding shelf.
Here is my mod to add an additional shelf to my Ikea Detolf.
8-32 threaded rod cut to 12.75"
Nylon L brackets
Glass or Plexiglas cut to 15" x 11.5"
I got everything at Lowes, but they are common parts to any hardware store.
Attach the threaded rod with the L brackets as shown. The little cylinders are to keep the glass off the threads, but are not essential.
I have one or two Detolfs.....
I would highly recommend getting some helmet stands (chrome kitchen towel holders) for your lids.
There was a guy on here that joined 2 together, it looked pretty sweet.