Derek,
I agree with Marck,
Grant will give you the biggest bang for your buck.
The only reason why I'm not going that route is because I'm going to build wood awning windows.
I found mine at one of those van conversion shops brand new in boxes but old stock, the guy gave me a great deal on some expensive windows that they would not use anymore.
Just my 2 cents worth
Any Local Building supply that sells "Sheds or Shed Kits" In Pa. I used 84 lumber, but Lowes, Moore and many others use them. Phillips is the brand name that I got. Shed windows are about $30, 1 or 2 louveres in silver, brown or white.
I used a 16" x 16" jalousie vent out of a glass block window. I cleaned it up and it looks and works great.
http://pg.photos.yahoo.com/ph/ahjones3/detail?.dir=ebd1&.dnm=4b0b.jpg&.src=ph Now I just need to find one for the other door. They quit using these up north here about 20 years ago. Now they use a insulated glass white vinyl hopper unit. Yecch.
Al.