After reading some of your other post I see that you are interested in some of the more difficult projects. When starting my search for a project I to was possessed to build a particle accelerator, similarly to you. This would be an extremely difficult project and I assume that you have already been told time and again that this is unrealistic.
Before I dash your hopes any more I will say this, although improbable, it is possible. Although you will not be able to build a particle accelerator like the LHC or Tevetron, there are several smaller versions that are, under the right circumstances, possible for you.
The most basic accelerator would be a cathode. These are used to accelerate electrons to low energies and are found in old T.V.s. Even this, though, requires a vacuum, which is reasonably hard for a high schooler to obtain.
The second is a Van DeGraff accelerator. This is built similarly to a normal Van DeGraff generator, except that it uses the built up charge to accelerate particles. This also requires a high vacuum, as well as an extremely high voltage.
The third type of accelerator that I have come across is the cyclotron. Probably the most popular of the DIY accelerators, it uses magnets of alternating charge to accelerate electrons in a circle until they are aimed into the target. Online there are several articles about people who have made these on their own using parts that they have managed to scavenge from all sorts of unusual places, sometimes going from door to door looking for the one piece that they are missing. Again, this needs a high vacuum, high voltage, and many uncommon materials.
Although these are difficult to make you may be able to make them if you have the right resources and connections. A couple of years ago there was an article about a seventeen year old boy who made a fusion reactor, albeit he went to a school that shared a campus with a college and worked with the professors there. Actually, I think I saw some of his posts on this site once, you might be able to find some advice in his posts.
From your other posts it sounds like you are interested in teaching yourself physics. The Dover series is cheep and give lots of good information on a wide variety of subjects. Some of the information may be outdated but it is still very useful if you are trying to teach yourself. They do require a previous knowledge of calculus and differential equations, but many of the math concepts can be picked up from the book while learning the physics.
So accelerators are an option, albeit a highly unlikely one. Do not start one if you do not have access to the materials, do not have enough time, or do not have the guidance. I do not know your specific circumstances, but would discourage this if you do not have one or more of the things mentioned above. Again, I would like to hear what others have to say about this.