3822sean wrote::? $$$$$$$$$$$$$ wow that buys alot of wood
For me it bought peace of mind, and a relatively "easy" installation.
I wasn't sure of my own personal construction skills/knowledge to make something that would function properly (not to mention air & water-tight)...coupling that with the cost of acquiring two sets of windows, latches, locks, handles, hinges and anything else I left out, and it was the safer way for me.
Yep, certainly a big bite in the wallet all at once...but the time involved to research how to do it and then construct it (again, for me), while adding up the cost of acquiring all the parts, and it was my best route. (Note: "my" best route.)
All the best!