Cutting the object from a given height

I’m trying to cut the model by adding a plane but I couldn’t find any function in python for such a thing. Please let me know if I’m missing anything.
I even tried clipping the plane in order to delete but it only delete’s from the view prospective and the object is still there in the behind.
Is there any other better way to do this ?
The image (Capture 04) is the actual structure of the building and the image (Capture 5) is the expected output. I want to cut the top portion of the building and also I want to make a hole in the structure, just as shown in the image (Capture 5). I’m able to perform this operation from the GUI but I don’t see any function from the python side.
Any lead will be appreciated.

You didn’t give us much info on what you tried and what isn’t working. There are for example rhinoscriptsyntax methods to do Boolean splits and differences, there are also RhinoCommon methods to do the same. If you can post some example code of what you are trying to do and perhaps a file with the objects, someone can have a look.

Yes I think a Boolean union of the cylinders followed by a Boolean difference with the cuboid could be a solution