A continuous flat roof roughly 6,300 m² in area with a single change in level extends over the entrance hall, debating chamber and presidential tract. The roof structure consists of a steel framed grid (with axes at 6-12m centres) supporting a glass top-light construction that allows daylight to enter from above. Surrounding this are areas of ribbed sheeting with a layer of reinforced concrete on top. In this way the advantages of a composite form of construction are employed over extensive sections of the complex. Over the debating chamber, the steel grid is suspended from large-span welded plate girders that also bear the loads of the adjustable acrylic louver construction.