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The Miter Two Roof Slabs tool allow you to bring two Roof Slabs together with a smooth joint.
The tool has a single option in the local menu:
By Intersection
Use this option when you are mitering two intersecting roof slabs. Both roof slabs are trimmed along the intersection of their perimeter lines. Vertices are added or removed as required. The new edges of the roof slabs are set to angles required for a true miter cut. If the slab thicknesses of the two edges are different, the angles will be different You cannot use this option if the slabs do not intersect.
To Miter Two Intersecting Roof Slabs: 
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