Making flat, raised panels, eh? Here's what I would do, in your situation.
First make a layer in solid medium gray, then put it underneath your UV map layer that outlines the model. Make a new layer for the raised panels. Grab your polygonal lasso tool and make a selection the size you want. Then fill it white, at about 20% opacity. If you want it to be higher, increase the opacity so it's a lighter shade of gray. Do this for all your panels. If you want more panels on top of the original ones (for a ziggurat effect) lasso again and fill again in 20% white.
Now, invert the colors on the UV map (so it's now white instead of black.) Make a new layer for the seams and details. Grab your paintbrush tool in black at about 20% opacity again, and trace the lines you want to be engraved into the panel. Again, the greater the opacity, the deeper the grooves. When it's all done turn off the UV map layer, leaving your shading on a gray background.
You can also invert these to make inset panels, or raised ridges, on your model, by darkening or lightening panels or lines. Think of your heightmap as a topographic map, where medium gray is the base level, white is the highest area and black is the lowest. If you were to make a height map for the planet Earth, it would look like this. See how the mountains are white, the plains are gray, and the oceans are black?
The height map's all you really need, as Photoshop's plugin will generate a normal map from it for you.