Lost Art Press (C. Schwarz) has published a book on traditional door and window making (original publication is from 1910). ISBN 978-0-9850777-8-5. It details on most aspect of sash windows, starting off with the case frames.
I attach an academic paper on making porch windows found in the Åland archipelago in the Baltic Sea. Sadly – and inappropriate for a publically financed academic paper – it is in Swedish, but there are quite a few informative drawings; and some of the shown windows are fascinating in their complexity (beyond what can be made with machines, according to the author).
The paper, and personal experience, holds forward the importance of finding knot-free, straight-grained dense wood. Plasters are also good to have around