Key plans are something that are included on almost all architectural drawing sets, and unfortunately Revit does not have a tool for this. Yes you could duplicate plans, and modify visibility graphics, but because you can only place one instance of a plan view on your sheets at any given time, you would have to create a key plan for every sheet where one is required. Instead, I propose the following method.
Duplicate one plan view and place the view onto a sheet. Scale the view to a key plan size (typically an engineering scale). While the view is on a sheet, use detail lines to trace the outline of the building areas you need. Keep in mind, you will not be able to snap to the exact building geometry, but this is a key plan after all. Now, you might ask, why not just trace the building geometry in the view. You could do that; however, that would make the following steps a little more difficult.
Now that the building areas are drawn, select all the detail lines you create on the sheet and cut them to the clipboard. Open a new generic annotation template and paste the detail lines in the view. Because we are using a generic annotation family for this scenario, it was important to draw the detail lines on the sheet in the step above. The generic annotation family does not have a scale - it is always 1:1 and sheet views are also a 1:1 scale. This eliminates the need for scaling the detail lines. Had we created the building outline in a modeling view, we would have to scale the lines down in our annotation family - which at best becomes an exercise in trial and error.
What I like to do next is create filled regions and text illustrating different work areas. I then assign these to Yes/No parameter so I can toggle them as need when loaded into a project.
I save my family to the specified location in the project directory. Load into the project and place onto sheets. If you are like me and want to have the key plan in the same spot on each sheet - no problem. Select the key plan annotation, copy to clipboard, choose Pase>Aligned to Selected Views. All your sheet views will pop up and using your CTRL or SHIFT keys, select the sheets that need a key plan.
Granted, there is little intelligence to this method as the key plan will not update with changes to the model; however, the method is quick and bypasses the limitations of making key plans from floor plan views.
Make it, don't fake it.