How to pave tile to the exterior wall?

When rendering, the outer wall will be transparent, and you cannot directly place tiles or apply materials. You can drag a floor, adjust its size to match the wall, change the thickness to 1, rotate it by pressing the X key, then drag it over and position it next to the outer wall. Finally, drag the tile/material to render it. (If there are doors and windows, multiple floors need to be combined to leave room for them.)