1) Place a motor inside an enclosed area (such as the closet inside my garage) in the center of the doorframe, about 3 off the floor.
2) Attach PVC or other mechanism which will push and pull the center of the door as the motor rotates. I used 3/4 PVC with bolts, attaching the main rod about 3-4 off center causing the total push / pull to be about 7 or 8 inches.
3) Combine thick foam to fill the door fram by pushing heavy gauge wire through the foam to hold it together. Allow the top and bottom wire to extend about 2 past either side so they can be inserted into holes in the doorframe (attaching the foam to the door at the top and bottom).
4) Attach thepush / pull rod to the center of the door, by drilling a hole through it and running the wire hold the foam together through it.
5) Dress up the door by applying thin layers of foam or other flexible material to the base foam with hot glue.
6) Attach a door handle, or create one from a wood or trim materials.
7) Paint it making it look aged and decrepit.
8) Adjust the motor speed (if you have a speed control) to a speed which you find acceptably creepy... And trigger the event or let it run continuosly.