TOPIC:

In order to select any object in either 2D or 3D view you must have the correct building, floor or layer selected as the current layer- ie highlighted red in the project tree.

Although most roofs are placed in the Attic it is always possible to move it (deliberately or accidentally) to another layer.

In the project you supplied, your roof is actually on the Upper floor and not the Attic, so you must have the Upper floor selected as your current layer in order to select it. The flat roof and porch are on the Ground floor.

Often in the 3D model i am unable to click directly on the roof to highlight it.