If You Keep Marmoset Monkey As A Pet What Size Cage Does It Need?

Despite usually being on the smaller side they generally need a larger habitat. You have to consider what they would be doing to occupy themselves in their natural habitat which is a great deal of jumping and climbing, foraging ect. You might have a smaller 'sleeping'  or cleaning cage (which isn't so small) or something but the rest is often at least about bedroom sized, double doors to prevent escape and also an outdoor area (attached to an indoor) usually.
www.junglefriends.org
www.simiansociety.org 
www.petmonkeyinfo.org 
www.monkeyzone.com