Cut out the two long outer walls. Fold the rooftops inward and glue the tabs at the corners of the roof to make two L-shaped pieces.
Then glue the two L-shaped walls together to make a rectangular box. Make sure the corners are all square 90-degree angles and the roof is level and straight before the glue dries.
Cut out the larger middle section of the roof and assemble into a rectangle. Then glue the two halves of the roof down flat.
Cut out the two shorter roof sections and assemble each. Then glue the tabs onto each side of the middle roof section. Press the tabs with a tweezer to dry the glue faster. Place the roof on a flat table as the glue dries to make sure each roof section is lined up along the bottom.
Finally, glue the rooftop sections to the roof of the lower walls.
Cut out the visitors and historical figures if you like, to place in front of the museum.