A drum kit is another name for a set of drums, so to ask what makes a drum kit is like what makes a set of anything, pans, golf clubs, its down to the individual to buy what they think is the perfect...
Well, Airfix models are called:
Plastic Model Kits.
There are many websites on the subject, just google 'Airfix Forum', or something like that.
Here is a brief word how:
The model is...
It's not really easy which is why most leave it up to the professionals to do the work for them but it goes mostly like this. First you have to have a clear picture in your mind of the kind of look...