Hi… Longtime subscriber and DIYer, first time poster here…  Am in the middle of my house remodel and am considering exterior trim options for my Milgard windows.   Dug thru my FHB archives and pulled a nice Aug/Sept 2009 article by Mike Vacirca about prefabbing the window trim using preprimed cedar.   The approach and look appeals to me as the head stands proud of the casings and overall, the frame stands slightly proud of the window. 

Wanted to take a similar approach, but one issue is that my installed windows sits 1 3/8″ proud of the plywood siding.  In the article Mike used a 5/4 casing since his window only stuck out 1″ from the plywood.   In my case, I would need to use a 2x board to be an 1/8″ beyond the frame.  Since I’d like to have a small reveal between the head and the casing am considering making the head out of the same 2x cedar material, but then backing it with a piece of 1/4″ plywood.   Hardishingle will surround the whole ensemble once all is said and done.   Good or bad idea?

Thanks!