It's a bitch, but this actually explains it decently enough:
http://www.wizards.com/default.asp?x=dn ... [br]Here's the short version: Figments can cover up, but not build in.
Example: let's say that there is a large wooden door with an ornate handle (that stick out 1 foot).
You CANNOT make the wood door look like an iron door.
You CAN put the illusion of an iron door in front of the wood door.
You CANNOT make the handle 'disappear'.
You CAN make an exact image of the door slightly in front of original door, without a handle.
You CAN put the illusion of a (giant python)/acid/spikes/flames on the handle.
You CANNOT erase the floor in front of the door.
You CAN create the image of a trap door in front of the door.
You CAN remake the floor (slightly above the original floor) with a pit (that has illusory depth).
To use your example, you may remake the wall as an illusion slightly in front of the original wall with a hole in it (similar to how you would add a painting of a hole in a wall), but you may not add a hole to existing wall.