Actually two questions.

I downloaded a map in game and got the idea to do something similar, but 3 floors tall, and some darkness.

1 - Holy crap did I get lost play testing my own level. Takes me awhile because I'm not using paper or anything. Just walking around trying to find my way out. Which is fine, because it gave me a little bit of a challenge. No way to pull up a map of where I am while I am play testing, right? I eventually got to the end, but that map would help.

This one is the real question I need help with.

2 - Is there a way to hide certain levels? Example:

http://i49.tinypic.com/15n900j.jpg

In that crappy photo I drew, it's a side view. The black things are floors you walk on. The orange is some lights on the top.

My problem is I completed my bottom floor you walk on. I placed the lights where I wanted on the bottom of the second level to light up the first. Now I completed the second level how I wanted. I want to attach lights to the bottom side of the third floor, but I can't see in there.

For putting the lights on the bottom of the second floor, I turned the map upside.. so it's like a top down view, and I was able to place my lights, but now I can't do that to attach lights to the bottom of the third floor because the other floor is in my way.

I do not know of a way to hide things in the editor. It has been stated that for complex maps not hiding sections whilst building is one of the small nags.

The only other thing I can think of you to try is to rebuild your map from the top down (start building level3 then level2 then level1). Maybe that might work ?

As RustyDios pointed out: Hammer has a much more convenient camera for that. However Hammer is a lot harder to get used to and it is a lot more complex to manage. But you can create even more awesome stuff with it than with the PTI

As for puzzling "where the potato am I". I personally hate it. A lack of light in area's is something I consider bad mapping. I personally prefer maps where you need to get your test element(s) and figure out how the hell they're going to help you solve the test. Not being able to see them because there is not enough light is something bad. (This is also the case for white textures appearing black because of the fact they don't get enough light.)

In response to the "where the potato am I" / darkness. This map isn't your traditional puzzle solving map. It's based on another map I found on the community. It wasn't super hard, but it was a fun little break from puzzle solving maps. On mine the difference is I added 3 floors and partial darkness to the mix.