Not my cup of java, but Fiddler's Green has some downloadable building templates that you can print out and assemble. They're reasonably priced (about $2 US or so), if you can handle paper buildings (I can't). The Z scale model is about right for microscale.
By the way, here's some advice from Luke Ueda-Sarson from the 6mm Miniature Yahoo Group:
The reason they 'look like paper' is not because they are paper, but because of the lack of relief detail.
Overhanging eaves are necessary to look like a building, yet many don't have them.
Having separate window sills, easy to cut out as just a sliver from a single sheet of card, can make all the difference by introducing some low relief. Thin wire for down pipes for guttering takes almost no effort, and can transform a building.
A judicious wash of very diluted brown or grey paint over the surface of the paper soo it looks slightly weatherw orn will vastly aid appearence.
But the most frequently seen problem is people failing to colour the edges of cut sheets, so corners and roof edges look horribly bright. Take a felt pen to the damn things so the edges don't stand out! It's bad enough with railway modeller's buildings in 1/76 scale - in 1/300 it looks plain awful.