what costume should i make for presentation about communism?

Castro is probably the most (in)famous communist alive today, particularly in the US. He's recognizable by a big bushy beard and a green shirt/army fatigues (and holding a Cuban flag doesn't hurt). Here's a picture:

I do not think that communists look any different from you or me and that you need any particular costume for your presentation. But if a costume is a necessity and your funds are quite limited, just pin a red star on the front of your white T-shirt and put on a black beret. The black beret became very representative of Ernesto "Che" Guevarra, one of the Cuban revolution leaders who practiced "export of the revolution" to other countries.

In a communist country, you have the VERY wealthy 1% (?) and the rest are dirt poor. Why don't you make most of your white T-shirt really dirty, and just a portion of it with glitter or something. That pretty much represents a communist country.

A Hillary costume.

you could be hillary.