This is the easiest junk model toy ever... Just take a box seal up the ends and make them smooth with a couple of cereal packet ends and then cover it in red paint (or any colour, colours or patterns you can dream up).
Then download all the J-Monsters in their windows here: J-MONSTER & BUS GRAPHICS DOWNLOAD.
Print them out (on scrap paper if you have it cos that's obviously the most eco-friendly thing do) and colour them all in with pens, paint, colouring pencils whatever you've got. Cut them out stick 'em on the bus and you've a double decker bus toy ... how simple is that?!