This, over here is my first attempt at a Matte Painting. Its taken me roughly 4 hours to make & has been a semi satisfactory experience so far.

I have managed to convert the first picture to the second Darker & murkier picture










Feel free to let me know about your views, you can check it out at Storm Through the Glass by ~rahulduggal on deviantART

Good work, but I think that the building is too evenly lit. Maybe you should try to darken some larger areas, like the roof and front. You could also set some tones to reflect the source light coming from the flash.
Also, the windows are giving the impression that the environment is still bright.

+1, funny but light troubles

As you see, the light comes from behind the photographer ; you added a thunderstorm, so you moved the light source... But you forgot to move everything

The manoir must be much, much darker, even with a massive backlighting... and it needs its shadow on the grass, which is also very bright, looks abnormal

I mean it should look like this :

(Yeah I did it fast, it's not perfect and I have no script to auto create thunders lol)

Still troubles : the wall is still too bright (but in fact it may depends of the type of the stone), and indeed the windows look like... sunny

You can easily correct it by, for example, creating a halo to simulate lights coming from inside the manoir.

If you want me to update the picture with the idea I suggest, let me know