I am a total amateur, Marc, and a cheapskate to boot. I basically used cardboard boxes to cut into the walls and roofs. Using pictures from the internet, I got ideas on how I wanted them to look and thought two inches per story was the right scale. I used super glue to put things together because it dries quickly and holds. Once the walls were together I drew in windows and doors. I then covered the structure with a mix of spackling, white glue which was watered down a bit. I was just looking for some texturing. The roofs were made by taking off one side of the exterior paper on the cardboard to expose the interior. I cut these into small strips and glued them into place. I am getting better at that with each go.
Once that was done I let everything dry overnight. The next day a spray painted in all in flat black. Once that dried, I did a liberal dry brushing in a fairly dark gray. Then I added some white to that and did a second dry brushing. Then a final dry brushing in white. For the roofs, I did a dark brown base, a lighter brown dry brushing followed by a final dry brushing of orange.
Another thing I learned as I went was to use scotch tape to cover the ends of the cardboard. The spackling mixture was to runny to actually seal the ends, and I didn't like the gaps. You can see the tape once the spackling and spray paint are applied.
Believe me, if I can do this, anyone can. And it's very inexpensive.
I have just added a post to my blog with some pictures that might be helpful.
winserswargames.blogspot.com