When you first get involved in go-karts, before you decide what sort of tires you want, if you want an off-road kart or an on-road kart, before you go shopping for a helmet to match that cool racing jacket, you're going to have to decide between investing in a ready-made kart or looking into go-kart kits. Each option has its pros and cons, and you might even say it simply comes down to personal preference in the end. Here's what you need to consider to make an informed decision.
The chief advantage of buying a ready-made go-kart is pretty obvious: it requires minimal effort on your part. You can buy it, put some fuel in the tank and drive it home if you want to. A ready-made kart is going to be made to professional standards, and it won't require any tools, assembly or, really, anything beyond a little maintenance now and then.
On the other hand, a big part of the appeal of go-karts is the fact that they're kind of a DIY hobby. There aren't many garages around where you can get your kart's oil changed, and the first karts were typically built from wood and junkyard scraps. Doing-it-yourself is the very spirit of the hobby for many.
A go-kart kit won't be a go-kart until you put it together, so it definitely retains the feeling of DIY without your having to go searching out any of the parts yourself. On the other hand, you can also use your go-kart kit as a starting point and customize as you go, switching out pieces for more high-performance parts (assuming you have a little bit of engineering knowledge). In other words, building a go-kart is simply more fun for a passionate go-kart enthusiast than buying one. Because of the labor required of the buyer, kits are typically less expensive than ready-made go-karts, as well.