Highlight the main roof on the building model and click to select it.
Slice roof revit.
Watch the status bar to be sure that you are highlighting the main roof.
You can cut openings in the faces of these elements or you can select the entire element to make a vertical cut.
Start points and endpoints can be added anywhere on the face of.
Click modify tab geometry panel cut drop down cut geometry.
Use one of the opening tools to cut a vertical or perpendicular opening in a roof floor or ceiling for example to accommodate a chimney.
The pick roof wall edges tool is active so that you can pick the boundaries that compose the dormer opening.
You can use the add split line tool to add linear edges and to split the existing face of a roof or structural floor into smaller sub regions.
This should keep you existing roof in tact and show a cut in the new construction phase.
Select a vertex edge face or point anywhere on the structural floor to start the split line.
Open the revit family with unattached voids and click create tab properties panel family category and parameters.
Hope this is of assistance.
Create a void extrusion and make to required cut in the new construction phase apply the cut and done.
If anyone is still looking for a solution you can make a roof cut into an existing roof using component model in place.
Click by face or vertical.
Determine the length of the void ideally in 3d view at wireframe mode extend this in order to intersect the roof surface that will be cut use the cut geometry command and select first the roof than the void.
Valid boundaries are highlighted.
Whether you want a double gable roof with 6 pyramid shaped dormers or a simple gambrel roof the basics remain the same.
In the family category and parameters dialog select cut with voids when loaded and click ok.
Place the cursor in the drawing area.
Revit roof slope can seem complicated at first glance but by learning a few critical features you can create any roof shape you desire.
Select the floor to modify.
Load the family into the project and place it.
See hd version of video tutorial here.
