Laying out levels can be a pain, in fact it can be downright impossible if you don’t have some sort of editor.
I caught this very simple guide on to how to do this using Visio which is very interesting as it is a tool that so many people have.
Here’s the process in a nutshell, export the Visio document convert it to an .xsl file then convert that into a .plist file using a specific XML template and read the contents in using multiple NSDictionary’s.
I’m making the process sound simplistic, but there really isn’t much more to it than that, you will of course need to do your own coding to make sure your game knows how to handle the extracted data 
You can find more info about this process along with the tools used over at Funky Visions:
Using Visio To Write iPhone Apps. Seriously?
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