It is very difficult and time-consuming to make a Ghostbusters costume that is completely true to the movie. The plan outlined here is for a comparably easy design, one good enough to appeal to movie fans but easy enough to complete in just a couple of hours.
Get a tan or off-white jumpsuit in a thrift store. This can take some time, but it shouldn't be too difficult.
In a word processing program such as Open Office or WordPerfect, create a name tag. You can use one of the original ghost buster names, or your own name. For authenticity, use red letters on a black background.
Download a GhostBusters logo. Print out the Ghostbusters logo and name tag on T-shirt transfer paper. Look at a picture from the movie to make sure you have them about the right size.
Carefully cut out the Ghostbuster logo and name tag, and iron them onto the jumpsuit. The logo should go on the arm, in front of and slightly below the right shoulder. The name tag should go on the left side of the chest.
Add elbow pads and a white belt to the costume.
Build a proton pack. Many things will work for a proton pack. You can use a cardboard box, a large piece of foam block, or a rectangular waste paper basket, for example. Make sure that it is rectangular, roughly the size of a backpack and black. Add black paint as necessary.
Add straps to the proton pack. Cut the shoulder straps off of a backpack and duct tape them to the proton pack so that it fits comfortably on your back.
Make a proton wand. Find a space rifle at a thrift store or toy store and paint it black. Although this approach will not be completely accurate to the movie, it will look pretty good and take a lot less time.
Make a proton pack chord. Attach a vacuum hose from the top of the proton pack to the back of the gun with duct tape. Paint over it in black.