The block sheet is a full 1/8" thick basswood(?), so one has to be a bit of careful to get openings correct. Once laid out, I use light pencil lines to layout the openings. I then make little circles in the corners as a locate point and drill them out close to the edges as I dare. Read - where ever the drill bit decides to make a hole with in the lines. Then I take an X0Acto hole saw and connect the dots. I then choose whichever side the saw got the closest to as my vertical base line. These windows span horizontal joint line to joint line, so that really helps. Then, carefully crave and file one side first and ensure that it is as straight as possible, then move to the other side and do the same until the width is just slightly tight on the window frame. Then do the same on the top and bottoms, but as these are with the grain, they are much easier. When they get installed, I'll need to find a spacer for to center the depth in the wall.
The left side pencil line is for the exterior staircase. This will be made out of clapboard siding.