Reduce a model down to a simple massing/mesh

Yes the layers are directly imported from revit too (ie. window frames, glazing, walls, etc) the thing is that they all come in as groups or components and literally all I need is the outer 2D shell. The revit model export is still very big for what I am doing even with interior elements turned off. I don’t even really need wall thicknesses. This guy on this forum seems to be wanting to do exactly what I need but no one could really help him either Create an outer shell from complex model

I am starting to lose hope on it