Here are some more screenshots showing my progress on PBR. The following screenshots show a metallic surface using different settings of roughness.

Physically Based Rendering 1

Physically Based Rendering 2

Physically Based Rendering 3

Physically Based Rendering 4

Physically Based Rendering 5

Physically Based Rendering 6

Here are some screenshots using normal maps

Physically Based Rendering 7

Physically Based Rendering 8

Physically Based Rendering 9

Physically Based Rendering 10

Physically Based Rendering 11

Physically Based Rendering 12

TODO: Write an article/tutorial about physically based rendering