Lets say you have three buildings on your site and they are all at different angles. If you go to View Properties you'll notice that for orientation you only have a choice between Project North and True North, but what if you need to work in plan views that are orthagonal to each building?
Just setup duplicate floor plan views for each building and turn on your crop regions. Select the crop region and you can rotate the view to any angle you need. Because you've created duplicate views you can now preserve the different angles in each view for all time. Keep in mind, Revit will rotate your view in the opposite direction that you rotate your crop region.