Bones;
My first paint caddy was a simple tackle box from the sporting goods section. The type I had was the multi layer and hinged type. It held all the paint bottle types and sizes. I labeled the levels and pulled out what I needed then secured the rest.
Another way is to use shoe boxes cut down to the height of the bottles.
Take the tallest and/or most common size bottle you have mark a pencil line even with the top of the bottle on the four sides of the box. Trim the box down with a straight edge and knife or scissors. Place the bottles inside and close the lid.
Another is go to Wal-Mart or department store that sells large tupperware or sealable storage boxes. Find a few that you can stack. Divide the inside with foam board dividers like a case of beer or wine (slotted squares) and place your paints in the areas created. Label the tops or fronts whichever side will be most visible.
Now that I have a dedicated 6X4 workbench I have custom built my shelves with each type of paint in a row at the rear of the bench.
You should have seen my first bench! It looked like a second hand furniture store had exploded.
I used a POWDER BLUE bedroom door layed flat for the bench with two matching night tables as the pedestal legs (four drawers in each) RED Body with WHITE Drawers and a pair of matching bookshelves Highway sign Green these were mounted on the ends of the top with a shelf between them and to that I undermounted a light.
Just thinking back on it gives me nightmares. But it served a purpose and quite a few goods kits came off the "Frankentable"
It finally met it's demise in a tragic chainsaw and bonfire accident.
I hope some of these will steer you in the direction you want to go.
Cheers;
Gregory