Here's something else you can try, Mayastatic...keep in mind, this is just a basic idea; you can exploit it and manipulate it however you see fit ^.^

1) create a simple cube, scale it up by about 5 in all directions.

2) translate it down in Y so that its uppermost face is BELOW the grid origin.

3) in the top view, use the custom polygon tool to create some random shape...it doesn't matter what, but make sure it "fits" the size of the cube face.

4) select the polygon face and the cube and combine them

5) change your select-by-type to faces, and select the poly FIRST and the cube's face SECOND

6) Edit Polygons -> Make Hole

You'll notice that it has multiple operations...fiddle around with them, it'll be pretty obvious as to what each one does.

Happy hole-making ^.^