I don't like to stack materials, because hard to find the right size (and length). I decided to stock small diameter round/square stock based on length/grade system.
I use paint or colored electrician's tape to mark two grades of tempering steel and silver steel from other drawn steel.
Short stumps are kept in boxes, for some reason I seem to accumulate more aluminium offcuts than steel.
1: Next place is upright rack, that has about 300/600/900 mm pipes in 3x3 configuration, I collect there all odds that I need randomly and never remember if I have them.
2: I tied together with wood frame and hoop bunch of drain pipes, all 700 mm long (same length than depth of the storage unit). I keep there certain material that has fairly immediate use or is for next project.
3: up to room height stock (mainly key stock and mystery steel from junkjard) is kept on a rack that has gates (swing up) to prevent rods from falling. This works pretty well, because all can be very upright without any risks.
4: Most valuable rods are in a box that is atop of the storage self. This rack is such way that it is easy pull out single rod, and it does not use much space, because I left enough height for standard storage boxes.
I tried the standard rod rack approach, but it worked badly for me. I was having a lot wasted space, clutter atop of stock, I had to rummage trough and hard to keep order of different lenghts.
Pekka