To assemble the mansard roof, the tabs of the mansard sections (the side pieces) are glued under the flat roof section for the top. When this assembly is dry, the entire roof is glued to the upper edges of the main building.
Test fit your roof sections on the building to set the angle you want for the joins of the mansard. When you have the corners the way you want them, join the mansard sections together. When the mansard section is dry, glue the tabs at the top edge of the mansard to the underside of the flat roof section. Set this roof assembly aside to dry. When it is fully dry, apply a bead of glue or a line of glue from a glue stick to the top of the supporting walls and glue the roof to the top of the walls. Leave this to dry before you add any second story sections to the top of the flat roof.
