Filament Storage Racks to be mounted on a flat surface. Requires a 24" deep flat surface for 2 rows. I use a set of shelves from Sam's Club for my printers and filament:

https://www.samsclub.com/p/members-mark-5-shelf-storage-rack/prod19280016?xid=plp_product_47

These are designed so that you can use almost anything for rods. Round, square, angle iron. Pretty much anything that is ½" -1 ¼" in diameter will work for the rods. I used some 7/8" heavy duty curtain rods for some, and some ~ 1" metal poles from a Harbor Freight portable shed for others.

Assembled with #8 dry wall screws that you can pick up at any hardware store, in the US at least. 1" long screws to mount the pieces to the flat surface. For mounting your rods, the length of screw needed depends on the diameter of your rods. I used 1 ½" long screws for both my 7/8" and 1" rods.

There are short end pieces for your front row, and tall end pieces for the back row. There are both short and tall middle bridges. The tall bridges do have holes so you could drill into your rod and screw a 1" #8 screw into them, but it isn't required. Some of my bridges I screwed to the rod and some I didn't.