Buy a good quality 10 or 12 inch ceramic flower pot with two saucers. We'll discuss later why two saucers are needed. Next, you will need sand; enough to fill half of the pot. This will be the main components for the flower pot grill in addition to charcoal, skewers, and something to cook.
Warning: I mentioned that the terracotta of the flower pot will insulate your grill. This doesn't mean that the vessel won't become hot. It will get horribly hot and should be placed somewhere stable and safe. At all times, someone should be responsible for each pot you put out, until that pot's fire is extinguished.
A good pot shouldn't have any cracks. Cracks can cause your pot to break when filled with burning coals, and that would be bad.