First, paint a medium grey on your canvas.
Now create a new layer. Here we'll paint our first layer of panels.
First, we'll need a panel brush. Find one of the default photoshop
brushes that is square, I found them under the "Square Brushes" brush
Now lets customize the brush. First, change the spacing to a much
Under Shape Dynamics, increase the size and roundness jitter.
Turn scatter on, and increase the amount...
Now paint with the brush using the mouse with a slightly lighter
grey value on your top layer until you get some panels...
Now with that layer selected, go to Layer -> Layer Style ->
Bevel & Emboss. Play with parameters such as Style, Technique, Size
and Shading Angle. Remember, be a little bit subtle, the default values
may be a bit too strong.
So this is giving a little bit of 3Dimensionality to your panels,
basically, it's simulating what light might look like hitting the
beveled edges of the panels.
Now it's time for shadows, lets fake an ambient occlusion pass using
Outer Glow, but instead of a light glow, make the glow dark...
Set Blend Mode to Multiply, Opacity to something low like 20%, color
to black, and Size to 9. If you make the size larger, the panels will
seem to be higher off the floor. If you make the size smaller, the
panels will seem more flush with the floor.
Now lets duplicate this layer, clear the paint (but leave the layer
styles), and paint more panels of a different size in a different
color. I did 3 layers of panels to achieve this.
And remember, you don't have to only use the brush. Anything that's
on that layer will get the bevel and also the shadow. So you can use
the rectangular selection tools to select a random looking area, then
fill it with grey, and make panels that way. Here's an example...
This is 3 layers ontop of each other using the selection tool. Also, as
well as the "Bevel and Emboss" and the "Outer Glow" styles, I added a
"Drop Shadow" style as well. So now I have shadows from an ambient
light (the "Outer Glow" style) and directional shadows from a key light
(the "Drop Shadow" style).