In fact, the only sizes known to the script are the height and width of the output, in this case A4 landscape. You're free to redefine those sizes if you want to make different sized booklets, like A6 ...

Using the default values, the example below will create an portrait-oriented, A4-sized map of Bangkok at scale 1:25000 ... papermap latlon \ --tile-server "Stamen Terrain" \ --size a3 \ --landscape \ ...