It is best practice IMHO to model one building per file, modeled orthogonally, in whatever orientation is desired for construction drawings (even if you don't need them).
All buildings are then linked into the master plan / site file, where they can be oriented properly and have their heights changed as necessary.
There are many threads over the years on this topic. If the story count is similar for all buildings, you can hotlink the individual building PLN files into the master plan file and then move the stories to where they belong vertically in the 3D window (e.g.). Solid element operations may be lost, but you have full layer / layer combo control over all buildings at once in the master file. Because everything is hot linked, any changes to any building's file will be automatically reflected in the master.
The oldest way of creating the master plan is to save each individual window as a custom GDL object (open the 3D window with the desired content visible, view from the top, and libraries and objects > save as). Then place these GDL building objects into your master plan. They will be monolithic objects with no layer control, but the floors will be glued to each other and so you can just move the buildings up and down and rotate them to their proper orientation. if the buildings will be changing, do NOT save these objects as embedded objects in the master PLN, but instead keep them as links to the GDL gsm files on your disk. Then, if you change a building and re-save the GDL file, over-writing the prior one, the new content will show up in your master PLN.
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