It's simple really. Once you build your first one, you want to build a second to see how much better you can do. As far as kitbashing, that's taking a standard off-the-shelf kit and redesiging it. For example, you bought a Kadet Sr and redesigned it into a twin with the engines mounted on the wings. This takes a lot of preplanning for things like trust angles, single engine flight due to differential thrust and so on. For a beginning builder, staying with a stock build is the way to go for the best chance of getting a plane into the air