Cut out and assemble the rectangular box of the Dag Hammerskjöld Library building. If you'd like to add more detail to your model, you can cut out the thin upper level of the library. Note that the two long sides of the piece have a slight concave curve. Fold the upper level into a rectangle and glue in place on the rooftop of the library.
Cut out the rectangular roof piece and roll it against a round pencil to give it a slight concave curve. Then glue it in place on top of the upper level walls.