The best method would be separate plans and then hotlink them together in a site plan.
But now you have them together already you can use layers and multiple drawings on layouts to achieve what you want.
Here is an old post where I described this method for producing isolated room layouts.
This will be the same situation you have with the adjacent buildings.
http://archicad-talk.graphisoft.com/viewtopic.php?p=182148
Using white fills is another method where you won't need multiple drawings on the layout - but I find you are constantly battling with display order of what is in front or behind the fill.
Barry.
One of the forum moderators.
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