also its website: http://www.cosmicwatch.lns.mit.edu

In terms of difficulty to build and operate it, I would rate the discussed projects such: cloud chamber < DIY particle detector (electron-detector variant) < DIY particle detector (alpha-spectrometer variant) < desktop muon detector

Even DIY cloud chambers can be a bit tricky to get running for the first time (especially with too high humidity like in summer). Just don't give up! ;-) A few tips can be found in this manual: https://scoollab.web.cern.ch/cloud-chamber