Click modify tab geometry panel cut drop down cut geometry.
Slice roof revit.
This should keep you existing roof in tact and show a cut in the new construction phase.
Click modify floors tabshape editing paneladd split line.
Place the cursor in the drawing area.
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.
Click by face or vertical.
Select a vertex edge face or point anywhere on the structural floor to start the split line.
See hd version of video tutorial here.
Revit roof slope can seem complicated at first glance but by learning a few critical features you can create any roof shape you desire.
Watch the status bar to be sure that you are highlighting the main roof.
The pick roof wall edges tool is active so that you can pick the boundaries that compose the dormer opening.
In the family category and parameters dialog select cut with voids when loaded and click ok.
Create a sloped roof in revit step 1 draw your roof step 2 define the slope.
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.
Hope this is of assistance.
Select the floor to modify.
Valid boundaries are highlighted.
Load the family into the project and place it.
Create a void extrusion and make to required cut in the new construction phase apply the cut and done.
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.
Open the revit family with unattached voids and click create tab properties panel family category and parameters.
If anyone is still looking for a solution you can make a roof cut into an existing roof using component model in place.
Start points and endpoints can be added anywhere on the face of.
Whether you want a double gable roof with 6 pyramid shaped dormers or a simple gambrel roof the basics remain the same.
