It needs to be poker table height, be amenable to adding wheels, needs to be enclosed (the side access door above is perfect) but front access is OK too. Needs to be somewhat rectangular as above as opposed to square. Would preferably be a simple laminate and must be wood, not metal.
This shows one of the carts I made from an ikea rolling drawer/cabinet. I also had a taller one from a kitchen cabinet. Not sure if I posted that here.
Here is the link to the ikea "kitchen cabinet"cart. Since you will basically cut a custom top no matter what, honestly you can figure out what size you need the base cabinet and it wouldn't be too terrible to just trim it down - you would also of course need to trim down the "door" and just make sure to have it such that the hinges will still fit.