You know, I think it's the height of irony (yet again) that GW has these nifty looking buildings for CoD, and then they go and put them on MDF bases. Sure, it looks pretty, but take a look at the finished modular layout galleries in the second link. Every one of them makes a layout that doesn't comport with the building placement guidelines in the CoD book. Each layout is as wide open as the terrain that I have seen in most standard games of 40k. At that point, why even bother with CoD rules?
EDIT ==> I'm not saying don't use a base. I just saying, don't make it so big that it thwarts the intent of terrain placement between 2" and 6" apart.