Use this procedure to trim a slab or roof slab using a polyline, wall, roof slab, or slab to define the trim plane.
The trimming object itself does not need to intersect the slab or roof slab, as long as it projects an intersection in the current user coordinate system (UCS). However, the trim plane must intersect the slab or roof slab perimeter line; you cannot trim only the overhang.
Any fascia or soffit profile that intersects the trim plane is trimmed at the same angle as the slab or roof slab.
If the trimming object is a wall or a slab, the trim plane is at the closest surface. The new edge at the trim plane has its edge angle defined by the trim plane.
Trimming a slab to a wall
Trimming a roof slab to a wall
- Select the slab or roof slab to be trimmed.
If the object selected is… Then… a slab click 
. 
a roof slab click . 
- Select a wall, a polyline, or another slab or roof slab for the trimming object.
- Select the side of the slab or roof slab to be trimmed.