This can be done under Adobe Illustrator (and then optionally placed in the Photoshop document). This effect is called oblique projection. Here is the final result:
I've created an Adobe® Illustrator® Plug-in called Oblique Projection 'opo' to automate the creation process of Parallel 3D Effect (Extrude Effect). It is quick and gives you full control over the appearance of the extrusion.
Everything is on one layer so you can easily separate it from the rest of the artwork. Plus it is divided into logical parts - this way every letter (or even every part of the letter) can be modified fully independently.
Here is how I would create the effect you are asking for:
a) install ‘opo’ extension (free evaluation copy available here:
b) add extra point to the lower, right corner of the rectangle (using ‘Add Anchor Point Tool’):
c) select your rounded rectangle
d) go to ‘opo’ panel, type (for example) 20px for X and -20 Y direction. Select Projection Z-Order ‘Z-‘, and ‘Solid’ Projection Type. Choose ‘Custom Projection Color’, put 153, 153, 153 into fill; leave the stroke blank (0).Hit ‘create projection’:
e) Finally, select the right side projection objects, and modify its color: