I've been working on kitbashing some 15mm scale buildings for use with my recently painted Critical Mass Games miniatures. I'm using the excellent Urban Mammoth Platform Builder: it's so versatile that you can build almost anything you can think of. Here's my first attempt:
At £12 for 13 sprues (which would be enough to make several buildings like the one above, the Large Platform Builder box is great value. I will definitely be buying more!