Computer case (also known as computer chassis) comes in different form factors. Form factors refer to the size and shape of the case.
The key factors in selecting a good case are as follow:
Size and Ventilation:
Computer cases come in different sizes such as; Micro ATX, Mid-Tower and Full Tower. When shopping for computer case make sure the case is large enough to fit all your components inside and make sure you still have some room for future upgrades. For example, high-end graphics cards which are longer than usual won't fit into some mid tower cases. The number and size of the drive bays that can fit into a case is also important. You will need 2.5"/3.5" bays for SSD/hard drives and 5.25" bays to install a Blu-ray/DVD drives. Make sure your case is equipped with multiple fans and good ventilation in front and back to allow better air circulation through entire case.
All cases can support one or multiple Form Factor to fit Motherboards with different shape and size. For example, if you have an ATX motherboard, then you must choose a case that supports an ATX motherboard. Some cases are designed to have multiple holes on the motherboard tray to hold almost any motherboard as long as their size is supported.
Case Appearance and Material:
The appearance of a computer case doesn't affect your gaming performance but if you don't match the colour of your external components with your case colour and layout then you will end up having a bad looking gaming computer. Some cases have included clear side panels or acrylic windows so that users can look inside while it is operating. Cases are usually constructed from steel (often Electrically Chromate Coated), Aluminium and Plastic.