I have been experimenting more with the authoring tools and figured out how to make a false wall. But I'm not sure if it is a good idea or not? What do you all think about a false wall mechanic added to the game? Like a Aperture Science Holographic Device (I'd imagine it would be named like that)?

You would need a projection, like the one in the credits., or it would confuse the player

I feel like it would confuse the player no matter what...

And what do you mean a projection like the one in the credits spongy?

I meant like the lines that run down like on the computer monitors or static with an opacity of 10 to make it look fake.

So basically, player's would need a way to distinguish a real wall from a fake. But it can't be too easy to see because that would make the fake wall worthless.

Though if the fake wall had no sign, it would make the player confused

No offense, but the whole idea seems a bit worthless in a puzzle game like Portal. It sounds like you either want the player to run around until they figure out they can walk through a wall or try to avoid falling through invisible holes in the floor. This doesn't sound very puzzle-y or fun. Props to you if you figure out an intelligent way to do it, but it seems like an extremely limited mechanic (and more of a gimmick than that).

I respect your opinion Random. Perhaps I should explain myself even further about this. I was playing Super Mario 64 (not the DS remake) the last few days, and came across the mirror room that reflects things that are covered by an illusion (Snow Picture World disguised as a wall). So that got me thinking, why not make something similar?

Dr. Freeeemannn... I will... only.... let you do this if you use all Maaarioo...textures.... Why? .... Well, I'm not at liberty to say....

They, have a prop_mirror: http://developer.valvesoftware.com/wiki/Prop_mirror

Hey thanks spongylover123. I'll experiment with that later. BTW I am using a false wall in my new CTC map: CTC 3. But that's only for the secret trap I'm adding. Here's a hint if you are at all curious about it:
Hello! This is the part where I kill you!