How to Use Intersect Faces to Make Roofs in SketchUp
When creating roofs in SketchUp, you can use Intersect Faces to combine a whole bunch of gables, hips, dormers, sheds, and so on into a single roof. Doing so is no cakewalk, and it requires a fair amount of planning, but it works great when nothing else will.
The figure shows a complicated roof with several elements. Gabled roofs have been pushed/pulled into the main hip roof at all different heights, but edges don’t exist where all the different faces meet. In the steps that follow, use Intersect Faces to create the edges you want and then use the Eraser to clean up the mess:
Select the whole roof.
You can select the whole roof a number of ways, but one way that works well is to first hide the group that contains the rest of your building and then draw a big selection box around the whole roof with the Select tool.
Choose Edit→Intersect Faces→With Selected.
This tells SketchUp to go through and create edges everywhere you have faces that intersect — everywhere they pass through each other without an edge.
Get out your Eraser and carefully delete all the extra geometry on the inside of your roof.
This can be a lot of work, but it’s a whole lot easier than using the Line tool and SketchUp’s inference engine to figure out where everything should go.