Choosing a computer case

Choosing a desktop computer case is not as easy as it seems. A lot of people think it is just a metal box where you just chunk all the computer parts inside. In fact, choosing a good computer case requires knowledge of the size, internal space, motherboard support, power supply rating and etc. The following guide shows you how to choose a desktop computer case. Size of casing
The size of the casing determines how much space you need on your desk to place the PC. If you have a small desk with limited space, you might consider the smaller mini computer case. If space is not an issue, then you can go for the tower casing where there are more functions.
Internal space
If you are adding a lot of computer parts to your system, you might consider getting a tower case. A small, crammed up case will increase the heat generation and result in the overloading of the power supply.
Motherboard support
A micro-ATX case (micro tower) can only support motherboard of the micro-ATX form factor. If you have a motherboard of ATX size, get a mid tower or full tower computer case.

Tip: A mid-tower or full tower case supports both the Micro-ATX and ATX motherboard whereas the micro tower case only supports micro-ATX motherboard.

Power supply
Most of the desktop computer cases come with power supplies. If you add a lot of computer parts to your system, you will need to get a power supply with higher power rating to support the system. Here’s a quick guide on the power consumption of each parts:

Computer Parts	Watts
Motherboard	15-30
Low-End CPU	20-50
Mid To High-End CPU	40-100
RAM	7 per 128MB
PCI Add-In Card	5
Low To Mid-Range Graphics	20-60
High-End Graphics	60-100
IDE Hard Drive	10-30
Optical Drives	10-25

Do your own calculation and select the power supply closest to your need.
External USB and firewire support
Some of the desktop computer cases come with front USB, audio port and a firewire port support. This is surely a very convenient feature and should add in your consideration when choosing a computer case. I remember buying a cheap computer case without any front USB and firewire port, only to find that I have more USB devices than all the port available. I have no choice but to buy an extra multi-port USB adaptor and all the wiring makes my desk very messy. A good lesson learnt from here. Never compromise quality with cheaper price.
Cooling
If you add a lot of computer parts into your system or you are an overclocker, then you need to choose a computer case with good cooling system. A good computer case allows multiple fans to be installed and also openings to improve the heat dissipation. For more detail on cooling system, read the article on "Liquid Cooling System"
External feel
A computer case is no longer just a plain box. Nowadays, computer cases are well designed to create the ‘feel’ for pc enthusiasts. Some of the pc enthusiasts I know even modify their computer case (also know as Case Mod) to create the kind of "special feel". If you are interested to case mod, check out Xoxide.com for mod details.
Conclusion
The few points above are sufficient to help you choose a desktop computer case. If you are into overclocking or an avid gamer who owns high-end parts, you definitely have to get a computer case with good cooling system and high power supply. For daily usage, any case that is above $100 is considered expensive.