It depends. These sorts of projects are generally discouraged for a wide variety of reasons.
Most homemade EMP devices built by the everyday hobbyist are only designed to garble small LCD displays such as on calculators, and things like that. The amount of power necessary to do this is ridiculously high in most cases, and its inefficiency forces most people to just drop it and find a better project. That is really what I recommend to you--Find a different project.
If you plan on making a bigger one to destroy property or prank people, you border on the illegal there, plus it is far more difficult, if not impossible, to get a noticeable output.
So my personal advice: Just don't do it. It's not worth the time, effort, or money.