By default, a lower-story roof cuts around upper-story walls where it runs up against upper-story walls. You can adjust the roof to avoid saddle situations if you want. A saddle situation is one where rain or snow runs down the roof slope and collects in areas where the roof meets a wall. You can also have the roof ignore the upper-story walls completely.
To change the way a lower-story roof is created:
If you haven't inserted the roof yet, select in the catalog, then right-click and select Catalog Manager. In the Catalog Manager dialog, select Catalog > Element Properties.
If you have already inserted the roof, select the roof, then right-click and select Properties.
In the Roofs dialog, click the Solution Type button.
In the Solution Type dialog, click on the solution you want.
Click OK in the Roofs dialog.