I have 4 of these units plus 4 of the lower units.  The lower units all have casters which is great for cleaning out my garage.  I'm so mad that there are no caster options for these 4 units.  I thought I would have the option to purchase casters in the future.  They are built and in my garage.  I cannot paint behind them or clean under them without emptying each cabinet.  It's horrible engineering and design.  I'd prefer them to place a warning in them to place heavy items on the bottom shelf to prevent them falling over.