Building a kit vs buying a ready-to-run.
When you have the type of r/c vehicle in mind that you want to start with, the next big question is; kit or rtr. There are good arguments on both sides of the proverbial fence, but it all boils down to one question: what do you want to get out of the hobby?
The case for a kit.
If you enjoy tinkering and building, or know someone who is, then a kit is thew auto go. It's the ultimate way to customize each element of the r/c vehicle, from the radio to the chassis and provides a great way to learn the construction of your vehicle on an intimate level.
Building your radio-controlled vehicle from a kit is similar to building a scale model. There are many parts and pieces involved and it quickly becomes a labor of love and much focus to get things "just right". While the hobby started out as a kit-driven pastime, it has been slowly shifting to an ready-to-run world over the past few years.
Ready-to-run, right out of the box.
If you want to jump right into the hobby on the driving side, then an rtr system is probably the best fit. These packages come complete with everything you'll need, a radio, complete chassis, body, and charger. You can literally take everything out of the box, charge the battery and be on the road in a matter of hours (or minutes, depending on how fast your batteries can charge).
Just because you've purchased an rtr setup doesn't mean there won't be opportunities to tinker with and modify your r/c vehicle. Parts break, performance upgrades are desired, and general maintenance is needed on any type of radio-controlled car or truck. Believe me, there are plenty of opportunities to get your hands dirty with this hobby, no matter what setup you choose.
For a look at the kit vs rtr discussion from a performance and competition perspective, check out Josh Howard's "Fully Charged- A Racer’s Rants" article on RCNewb.com