As the publication will take the form of a newspaper, the size of the pages will be an important consideration.
The original size of a tabloid newspaper is 43.2cm x 27.9cm, however in the age of digital publications accessed through phones and tablets, an oversized newspaper would not be practical for the majority of readers. On the Paris metro system space is a premium, and so the newspaper should be smaller and more compact for it to a manageable for commuters and tourists who wish to carry it with them.
Also, as the newspaper will be printed in a Risograph, due the constraints of the machine itself the publication can be no larger than A3 in total size.
Considering all of these factors, a traditional tabloid newspaper can be scaled down using the same ratios to 2/3 of the original size, so the publication would be 28.8cm in height x 18.6cm in width. 2/3 is the largest size that would print onto an A3 sheet so that in the printing and cutting process, as little paper as possible is wasted.