Hi Doc Waldo, I've moved your thread to the 'How Do I?' section, hope you don't mind.
That dungeon looks like it might be Devin Night's work? It's beautifully done. To make a dungeon like this you need a couple of things:
1. Good floor textures.
2 Good Symbols.
Once you have the textures, the construction of it is actually quite straight forward since it's all on a grid. I know you're after something more detailed - hopefully someone will come and help. How advanced would you consider yourself in Photoshop? What version do you have? It might be worth putting that information in your personal details so it shows up under your name when you post.