Is there a way to cut this buildings top part. I tried split, trim, boolean commands but all of them failed. This is group and varied object. Explode and ungroup takes long time and make it difficult. Is there another way? I just want to slice and delete top of the purple plane.
First, is your object composed of surfaces or meshes? Meshes will not work with Split etc.
If they are surfaces, note that Split, Trim and Boolean operations will not work if complete intersections are not found. So when things fail, run the Intersect command and look at the result. If there are open curves, overlaps, etc., splitting may fail because Rhino cannot calculate the complete intersection to cut the parts.