here is all the parts needed for this section of the assembly. Please ensure the door hinge section is the one with the circle to the far outside of the part.
Arrange the parts so they look like the diagram. Note the windows are closer to the floor than the ceiling.
Glue around the outside edges of all the parts as shown. Not illustrated here is there should be a line of glue on the long sections of the door wall, much like the rear wall in this picture.
Just like the 1st floor, make sure the door is in place before gluing. It's very hard to get in after it's all glued.