I'm confused about what a shell is exactly. The documentation tells me that BRepBuilderAPI_MakeShell can be used to make a shell from a set of faces. But when I look at the constructor for MakeShell it asks for a surface not a face and it looks like it just wants one surface. Do I some how make a big suface out of my set of faces? Does anyone have a sample of code showing how to use BRepBuilderAPI_MakeShell to create a shell from a set of faces?