The long and short of how I did it is this: it's foamboard covered with spackle/drywall mud and the bricks are just random splotches of Miliput carved into bricks while the Miliput is still soft. Once dry I spackle the whole building and leave the brickwork exposed. Once the spackling has dried, I wet my finger and smooth all the dried spackle out. I do the roof seperate using hardboard as the base and a sliced up styrofoam ball (gotten from Dollar Shops) as the dome. Then spackle and smooth that out.
Next time I'm going to try using HO and O scale brickwork styrene sheet and see if that speeds up production a bit as I find Miliput needs overnight to dry. Too long for my impatient self once I get on a "building-roll" and don't want to stop.
-Todd