Ah, Ravells you are too kind.
It's not mine, though one or 2 very small details/objects might be mine.
I would think that there are tutorials to make dungeons like this, even if you take the basic ideas from gimp and use them in PS.
If your understanding of PS is good enough I think all you need is some time and practice and willingness to fail til you get there.
I would suggest trying something small. Two rooms and a hallway. Then if you get stuck, show a post and ask a question.