I'm no photoshop expert and I can't think of any tutorials off the top of my head. However, I would think you'd be able to do something with 'paths'.
Walls are not overly difficult, especially top-down views. A line of appropriate thickness with a pattern overlay or other filter to give it some kind of texture and then maybe a drop shadow to give it the appearance of height. The walls on my Arvaandor map use those basic techniques. Maybe that will help out.