First cut out the long beams that support the open space of the hall. For long thin pieces like this, it is often easiest to score and fold the pieces while they are still connected together. As one connected piece of paper it will be easier to fold a straight line.
After folding, cut out each beam. Fold and glue the piece flat. You may want to press the four beams under a book overnight to make sure they dry flat.
Assemble the large piece by folding and glueing the walls in place. Fold the landing of the stairs outward and small staircase downward.
Glue the four beams upright along the gray lines marked on the rooftop.
Then add the large landing and lower staircase that fits under the upper staircase.
Fold the square mechanical house and glue it to the rooftop.
Lastly, add the back staircase below the back doors of the building. You may want to strengthen the two tiny supports of the back staircase with a drop of super glue (as explained on the Tips & Techniques page) before folding the back staircase.