Well, I expect this is mostly hand drawn using a tablet and something like GIMP/Photoshop. I have little experience with Inkscape, but if you want Vectors, thats that you would use. I believe MOST of the way this make is constructed should be possible in Inkscape, but it will probably be somewhat time consuming. As for where to start, Ascension just recently created a tutorial for making houses. Thought it was written for Photoshop, many of the techniques can be easily incorporated into GIMP with some slight adjustments to create pretty much the exact same effect.