The windows and doors really finalize the outside look of the house. You want them to look a little rough so it's o.k. if they are shabby sanded after painting. The window frames are made of thin pieces of strip wood so a sharp knife is a must. It's about time to change the blade anyway. My wood pieces measured out at .6 x .3 mm for the frames and less than .2 x .3 mm for the glazing separators.
You can substitute match sticks for the separators if you have some and don't want to buy strip wood. Alternately, you can also cut your own strip wood to size if you need a piece but don't have the right dimensions. I buy large sheets of very thin (1/16th inch) balsa and cut tiny strips out for the window and door glazing. You can save a lot of money on those if you have a steady hand. They are about a dollar for a three foot section pre-cut. For one large piece of balsa ($2.99), you can get all you will need for several projects. You will need a lot of glazing strips.
My windows are cut from very thin plexiglass. My grandson gave me a huge poster size sheet from a recycled poster frame. It is 1/32" thick and cuts very easy with a box cutter knife. You may be able to find a poster frame cheaper than buying hobby window plexi. Measure and score twice and then turn it over, put a ruler on the cut line and snap it back clean to the size you need. You can also use heavy clear plastic cut from packaging. Both work just as well.
The first windows I tackled were the dormer windows. The measurements from the instructions in the book did not fit the way I wanted them to, so I used my own window measurements.
It's looking pretty good on the outside so far. But it's far from being finished. So many details, so little time!