Currently, there are two types of premade rooms: square and rectangle. Premade rooms have three pre-defined sizes - small, normal, and large.
Dimension and rotation can be set before adding a premade room to the scene.
Dimension can be specified in the length and width text boxes.
Rotation can be changed by clicking on the rotate buttons or by clicking on the numeric updown.
A premade room can be snapped to an existing wall. Wall snapping can be turned off by pressing the Ctrl key while positioning the premade room.