The tricky part of this build is the hanging geometry: a tall plywood unit carried entirely by trolleys on a metal strut channel fixed to the ceiling structure has to roll freely or it fights itself. That is exactly where the maker is wrestling now, and the way they are diagnosing it reads like good shop practice. Pushed from one side, the shelf binds and twists. Pushed from the middle, between the two rails, it rolls smoothly. Two mostly full five-gallon paint pails were added as a test and the binding stayed, which points away from simple weight as the answer.
The unit itself is a plywood replica of a designer's sliding bookshelf, and it does what such shelves are for: it glides sideways along the rail to reveal shelf tiers and wall storage behind it. Each side rides on two trolleys, every one holding four wheels in two sets of rollers. The shelf boards measure 12 by 21-1/4 inches, and the maker has confirmed the shelves sit level with each other, which is no small feat on a hanging unit.
Details worth noting: the front plywood panel bolts on near its top edge with six large hex bolts, nuts and flat washers in a horizontal row. That exposed hardware gives it a deliberate, industrial look, and in my view it suits the strut-channel support nicely.
The open question is trolley spacing. The maker suspects the close-spaced trolleys leave rotational play in the system, unlike the wider spread in the original design. The next set of shelves will get wider tracks, trolleys moved outward, and the maker has promised to report back on whether that cures the twist. I am genuinely curious to hear the outcome.