Recs.
Updated
The majority of drone hobbyists prefer to build their own quadcopter, either from scratch or through buying individual parts. They can be tailored for speed, strength or anything in between. This option will cover the pros and cons of a general purpose DIY quadcopter.
Specs
Pros
Pro Greater customization
By building your own, you have the ability to tailor your drone to what you want. If you need it to be faster, or more stable or more powerful you can choose the parts that will work best. It also allows you to use the parts you prefer, rather than the ones you would be forced to use by buying a prebuilt. This way you can mix and match parts to get the exact drone you want. You also have the opportunity to swap out parts to change how your drone flies instead of being constricted to the prebuilts exact type of flying .
Pro Usually cheaper
Building your own drone is usually cheaper than buying a prebuilt. Especially when first getting started, you don't always need to spend 800 dollars to get the job done. Even buying the kit version of a prebuilt is typically cheaper than ordering it prebuilt. This also saves you money because if you need to replace parts, you aren't tied to buying the companies proprietary(and usually more expensive) parts.
Pro It's a learning experience
Building your own drone can be much more educational and rewarding then just buying one and flying it. It allows you to learn about how your drone works and become more familiar with it which will help with repairing it and flying it. By buying a prebuilt, you may not gain the knowledge that will allow you to take full advantage of your drone.
Cons
Con Takes time and frustration
Building your own drone can be very confusing, especially if you don't know what you are doing or are new to the hobby. It will certainly take quite a bit of trial and error and triple checking everything. Be prepared to do plenty of research in order to get your drone up and running. An excellent article on getting started with some helpful tips and tricks can be found here.