For weather resistant properties. A new favorite is Ipe. very strong, hard and tougher to work with. You can get it in 5/4 decking and rip it up. Fir has always been a standard for wood windows. Redwood and Cedar are both very weather resistant but are soft. Cypress might be worth a look as well as White Oak.

There are a lots off woods that are good for window frames and sashes. If you want something easy to work then Fir is tops. Others that I have listed are great weather resisting woods. Some are harder to work with than others. For simple machining of window parts. Sharp tools and hard woods are always tops in my book.

Bill