Wooden windows are made basically the same way that kitchen or other similar cabinet doors with panels are made. While you can use mortise and tenon jointery, routed shapes with increased glueing surfaces are also common for wood windows. If you attempt these, be prepared to spend a lot of money on router bits. The sets sold for making full sized doors should have what you want.
If you have the typical storm windows like the ones used in barns, these are made with mortise and tenon joints but you have to watch angles closely. The bottom of the sash, for instance, is angled to match the window sill angle so water will easily run off the sill. Basically you can make these with a table saw and a mortising machine will help a lot.
One other issue for you might be the wood. Finding thicker than 4/4 clear pine might be difficult in home centers. This is one of those “but it seems so easy” projects that can be for someone with a bit of experience in woodworking. But if you are just starting, this will be a lot cheaper if you just buy one window.
Henry in MI
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