Building your own PC, as opposed to buying a premade one, can be a learning experience for anyone who hasn't done it before, and is sometimes worth it to do it just once for the experience. If you already know how to put a computer together, you might want to consider some of the other advantages and disadvantages of building your own PC before you make a decision.
Building your own PC lets you use the exact components that you want. Even with computer manufacturers that let you customise your machine, you can choose from a small set of component options, and they almost always have to be from certain component manufacturers that the computer companies have deals with. It can also take some time before the computer manufacturers have access to some cutting-edge components, while if you build your own system, you can use any component that you can get your hands on. Buying the exact components that you want also lets you determine the quality of all of the components in the machine.
When you build your own PC, you know that you can upgrade every component. If you decide that the computer needs more RAM or a new video card, you already know all the motherboard specifications and requirements, so you only have to purchase the correct upgrade and put it in. With a prebuilt computer, it can sometimes be difficult to know exactly what kind of cards and RAM the computer needs. Some manufacturers also use proprietary parts, meaning you have to buy your component upgrades through them, generally at a premium cost. If you build your PC from scratch, you know this will never be an issue.
The lack of an overall system warranty is one of the biggest drawbacks to building your own PC. While the individual components may come with a warranty, if one component fries another, you may have to fight to get the second replaced. Prebuilt PCs generally have a warranty that covers the entire system as a whole. PC manufacturers, or the retail outlets that sell the systems, generally have robust customer service departments and have a set system to handle customer complaints quickly, while each component manufacturer may offer a different level of service.
Disadvantage: Time and Effort
If you buy a premade system, you can take it home and have it up and running within minutes. Even if you have to order a system online, when it gets shipped to you, all you have to do is plug it in. When you build a system, you almost always have to order the parts and have them shipped to you, so you can't even start building until the parts ship to you. While there is nothing overly technical about putting a computer together, as long as you know where all the pieces fit together, it can still take several hours, as you have to find where all the screws will go to fit the different pieces together.
Advantage and Disadvantage: Price
Price can be an advantage or a disadvantage, depending on the type of system you want to build. If you are looking to put together a bare-bones basic system, you may be better off just buying a low-end one. Manufacturers get such good deals on the components and software that they can create a low-end machine for less than you can, unless you get some really good deals or use some used parts. However, if you want a cutting-edge system, it will be easier for you to find your own deals on components and avoid the manufacturer's markup on high-end PC items.