There are many ways to create a roof in Revit and one of them is to use an extruded roof. Unlike the footprint method, the extruded roof generally won’t match the footprint of the building. No matter what shape your building is, the roof you create will be rectangular in footprint as it is extruded horizontally across the building.
It will therefore be necessary to cut the excess from the roof, using the vertical opening tool. The below screenshot shows an extruded roof on a building that is not rectangular. We will trim off the unwanted corners.
To make it easier it might be a good idea to adjust your view range to a high enough level so you can see more of the roof you are cutting. It's also important to make sure you have the underlay visible along with the wireframe visual style to see the walls below more clearly. See below:
The next step is to use the Vertical Opening tool, which can be used to cut a hole in the slab object. In this case we are going to create the holes at the edge of the roof which will effectively cut the corners off.
The command can either be found on the Architecture tab in the Openings panel or by simply clicking on the roof - it will appear on the Modify Roofs tab as below:
When you set the command, you will be taken into Revit’s Sketch mode to allow you to define the boundaries for the required openings. As with the majority of sketched items in Revit, these boundaries need to be closed loops with no excess, intersecting or overlapping lines.
As you would expect, there are many ways to produce the sketched boundary, from lines, arcs etc, to pick lines that allow you to pick existing geometry.
Here I’ve used pick lines on the roof edges and pick lines with an offset for the wall edges to allow for an overhang. This method does often leave excess linework, but it is easily tidied up - in this case I’m using ‘Trim/Extend to Corner’.
You can see the results below, and please note that you can create more than one opening at a time.
After you have finished sketching, click on the green tick to complete the openings. You will see a warning if there are any issues with the sketch and the problem will be identified using the pre-set warning colour. Below I’ve added an additional line in to be flagged:
Once this is amended, or if no problems existed, you will see the results as below after you complete the command.
And here is the finished article:
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