I use a dremel-like tool. The brand is called PROXXON. German company. Very reliable lil machines. Bought mine 10 years ago and its still drilling and cutting like hell. Still a pain in the ass to cut 2mm thick brass! Same with bending it.
Yes CU is copper. It looks too dark to be brass but ok. I do HVAC for a living and we have to use a big sheet metal brake to get folds like that in the metal and huge shears to cut it. I can't imagine having to do it with a roto-tool!
Trust the chemist....it is brass ;-) copper would look red or brown. Not that golden. Depending on the patina.
Thats why I said its a pain to make these things! You have to use heavy sheets to make it stable. Thinner sheet wouldnt remain in its position, no matter how exact you bend it. Know what I mean?