For the “Fit for a Wren” article (read the original version here), I used a bandsaw to open up the cavity in the billets and to create the roof and bottom of this birdhouse. However, you can also make this birdhouse with hand tools.
Using a commonly available 28-inch bow saw, it took about an hour and a half to saw out the pieces for this nest box. As a test, I made one of the cuts with a hand ripsaw. It cut slower but made a neater cut and could certainly be used instead of the bow saw.
I used a marker for the layout only because the heavy lines show up clearly in photos. You should use a marking instrument (such as a scribe) with a finer point.