PC casings come in many different shapes and sizes, each with its own advantages and disadvantages. The five most common types are: ATX, MicroATX, Mini-ITX, Standard ATX, and Extended ATX. 

Each case type has its own set of features that you'll want to take into account when choosing one. For example, Extended ATX cases are the biggest on the market, but they also have the widest variety of features. Mini-ITX cases are the smallest but lack a lot of features common to other case types. 

ATX cases are the most common type and offer the most features for your money. They're small enough to fit on a desk but big enough to fit a full-sized motherboard and graphics card.