I just want to take some time to tell you that making buildings this way is a quick and cost effective way, and all you need are some basic tools.
Let me show you what I mean.
The current building I am/was working on is made up out of 3 blocks, of which the largest is show in the photo. In the back is the 2nd, smaller block, already made, glued and wrapped with 2 rubber bands to keep it all tight while drying. It also shows 2 of the 3 basic tools you need, a sharp knife (which needs to be replaced a lot) and woodglue. A metal ruler would be the third.
At the moment I'm not using templates, but make it up as I go along while looking at one or several pictures, or off a sketch I made. In the future I might make some templates, but since I'm doing everything of a basic set of measurements there is no current need.
A doorway is 15mm wide and 25mm high. A window for this particular set of houses is 10mm x 10mm. A normal level house is 40mm high per level.
Anyway, 4 blocks of 10x8cm form the basis for this house. The roof is a seperate piece of non standard size, but in this case 10cm x 9,4 cm (as you lose 3mm per wall). Scrap pieces are used to form a line on the inside 10mm from the top of the wall. This will become the support for the roof.
In the back of the photo you can see a H column made of strips of foam. This is used to support the roof of houses of a certain size or height. The roof is perfectly capable of supporting a full assortment of metal models, but to prevent the floor from sagging too much this ads extra strength for something that is made in seconds.
How this works is shown here:
And when reversed and glued to its base, it will give full support to the roof area.
I also add strips to the sides of 2 of the 4 walls, just for extra grip. Since I use very thin layers, 30-60 minutes of drying time is all you need, so if I have little time I just make the basic parts one night and glue them together on the next, or try and cram it all in one go. And by cramming I mean 90 minutes tops for one or more blocks.
Now windows and doors I do differently then most. When I look at others making these buildings I see removable floors and open windows, but I'm not part of that school, lovely as it looks though. I'm more cautious and want my stuff to be durable, modular and light weight. Open windows and doors tend to weaken a structure, so I glue doors and windows shut with bits cut from a cereal box.
This looks like this:
I put glue on the foam, press the cardboard on it and then use a toothpick to fold the woodglue over the paper, covering the sides and sometimes all of it. This soaks it in well and makes for a durable bond. But if you really need to, you can take a sharp knife and slide it between the glue and foam and then rip it all off, carefully. But a bit of planning makes sure you never have to do that.
Doors and windows can be made with just one sheet and painted black or like glass, and doors can be the same, black, weatherd metal, or, if you layer it with strips of cardboard first, (weathered) wood.
So now everything has dried, you got 5 parts, you just glue the sides, put them together and add a rubber band across the top where the roof goes first and then one at the lower end. Don't make them too tight though cuase they will damage the foam. I then leave these overnight to fully dry, or, when they need it, I add some more glue to the seams on the inside, and spread that out with a toothpick.
The next day I cut out a base, trim the sides, sand them a bit, score them with a sharp knife and apply glue to the underside of the model. Set down and wait another night. Give it time to set and don't be too hasty, you don't want to ruin them. Especially with the limited time that I have.
The next evening, or weekend, whatever comes first, I sand down the corners of the buildings with a cheap disposable nailfile and then coat them in Gesso with a big brush. Then use a smaller brush and fill in the sides and corners of the windows and doors. I use thin coats so 30 minutes later you can add another. I use thicker coats where buildings meet to strenghten corners or to cover seams. Set aside to dry while you work on something else, or read up on a forum, or what not, and I give them another coat before going to bed. Only takes a few minutes to do them properly.
Next day, sand the base, just plain woodglue over scored plasticcard coated with sand, and you are set for the next stage, paint. But thats for next time.