The Flaps are filled with an arrow pattern. The arrows point towards the edge of the flap that must not be cut.
All orange rectangles stand for holes and have to be cut out.
All red rectangles have only to be cut out when you build a certain version. A steel-ruler and a sharp modellers's knife are better suited for cutting the buildings than scissors. All flaps are folded away from the printed side. And the walls are folded at the respective corners. If the folding line is red than the paper has to be folded towards the printed side.