I've made potting on 'pots' by wrapping newspaper around a drinking glass and sliding it off. However the idea doing this is that the folds that make the base hold it together and stop it unravelling so to go tubular you'd have to think of a way to bind the edge to the tube. In terms of diameter I would think the wider the better really.
I collect all my newspapers by walking the length of the train before getting off on a friday night - proper recycling!