I felt that a decently accurate Arc Reactor should be easy to make by the average person, and should be constructed at least mostly using materials that are easy to obtain. Needless to say, I think the results are pretty good, especially for a first attempt, and you will be able to use my build to create even better results of your own.
Step 1: Set up the Game Plan
1) Lights: Every iteration of the Arc Reactor lights up; a ring of palladium undergoes some kind of 'arc reaction' (read: copyright of Stark Industries), glows, and is visible through the device.
2) Coils. The original purpose of the Arc Reactor is to power electromagnetic coils that prevent shrapnel from entering Tony Stark's heart. The first Ironman movie's Arc Reactor had 10 coils (and 10 spaces in between where light was visible).
3) Inner Ring/Bracket: It appears as though there is an inner ring assembly of some kind that holds the reactor together. It has 3 structures coming from the center separated by 120° and a series of internal rings that appear to provide structure for the apparatus.
At the very least, someone building an Arc Reactor would want to show off lights through a t-shirt, and at the most they want to show off the entire reactor. This means at minimum, we need to construct an even ring of light that appears to be covered by coils (or anything) with a glowing light in the center as well.
NOTE! In this build, I used a hot glue gun, soldering iron, and other assorted tools which are easy to come by, but DANGEROUS. I always solder on a wooden surface, hot glue over newspaper, cut in a direction away from my body, and other various safety things that may or may not be common sense. BE CAREFUL.