You can't have objects on multiple layers but as Stuart mentioned you can use the values of the MVO options in your object scripts.
This is fine so long as they are your own objects and you can alter them (and know how to do it of course).
I wouldn't recommend altering Graphisoft or 3rd party objects unless you duplicate them (save as) with a new name in a new library folder.
In particular the MVO option you are looking for is ...
REQUEST ("floor_plan_option", "", storyViewpointType)
This will result in a value of '0' (floor plan or '1' (ceiling plan) that will change based on your MVO setting.
You can then make your object show different configuration with if/then/else commands.
Or you can have even more control through MVO if you create your own Library Global parameters and use these in your scripts.
You can then control pretty much whatever you want - pen colours, line types, text on/off, even the size, font and colour of the text. And you can add parameters to completely change the way your object looks based on these parameters.
You can do all this individually in each GDL object but with MVO settings you can control them all globally.
But you need to know GDL scripting.
You can see examples of what MVO control you can have if you open the MVO settings dialogue and look at the section for the Graphisoft library objects - or of course the image that Stuart attached to his post.
Barry.
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