Thanks logesh, I apologise for the late response! As usual I'm using really simple materials and lightning setup - just a direct light that acts as a sun and a vray area light just infront of the door(works like a sky portal). 99% of the materials in the scene are blend materials and basically what I do is make the base material and then make another one which would be the dust material - Vray dirt in the diff slot and a normal/bump map of the alpha that I'm using later on to combine the two materials within the blend. And from there on it's just tweaking the curves, maybe the output of the alpha etc.
And a little update, hope you like it:
