I was trying to search for my post on my homebuilt cart, but apparently the old posts got lost in yesterday's forum upgrade. Here's a pic of mine:
I was originally going to use the HF 16"X30" 3-shelf cart, but came across a few 18"X24" heavy aluminum trays, so I built it myself. The bottom section is enclosed on three sides with thin plexiglass to keep my MF's clean, with a clear plastic curtain for easy access in the front and some foam board dividers to keep the mf's sorted.
The middle section has a few bins for applicators, but there's enough open space to set down a polisher or two.
The top tray has some sections cut from mailing tubes that will keep bottles from tipping when it's being moved or also serve to stuff in a towel that's getting reused, as well as some clay bars in baggies. They're held in place against the tray with binder clips. Scraps of various size plastic tubing are glued to a piece of aluminum to hold the small stuff, such as small brushes, swabs and polisher wrenches. I've been using it for about a year and I'm very happy with the layout so far.
I recommend getting the cart of your choice and before you get elaborate with design, do a detail or two as a test. That's what I did. I found my first priority was to have a mobile table, just so I have a place to set things down, rather than on the car or on the ground and have easy access to the things I grab on a repeated basis. I don't need to carry around the entire contents of my supply shelves. I'll load up the chemicals, tools or pads I need at that stage of the job, then refresh when I move to the next stage. I'll often use an LED spotlight in a fixture I can clamp to the cart and move around as needed as a swirl finder.
I hope this helps you in your design. Fell free to reply with any questions.
Bill