I made these window units earlier this summer, under a tarp in my back yard using all portable equipment. I used standard TDL single pane 3'x3.5' Brosco barn sash.

The siding they used is roasted Poplar.

The windows are made from Eastern Red Cedar, but it's really a species of Juniper, the same stuff used in closets.

I retained the band sawn finish and variation in thickness by as much as 1/4" while still maintaining tolerances around the sash of about 1/16", sufficient for felted wool weatherstripping.

More here: http://www.ryanolivieri.com/oper_jhw.php