I would not attempt this without some garment construction experience, I would look for a commercial pattern for a boxy jacket, like this one:
http://mccallpattern.mccall.com/m582...hp?page_id=115
Look for one with no darts or any seams other than the sides, suitable for quilted fabric. On the sample link above, I'd skip the collar and would not plan on button holes. You could use frogs or other fabric loops to make closures. Since you are only going to get one shot, I would make a sample jacket from the pattern using something like fleece to make sure the jacket will fit. Make enough cathedral window 'fabric' for each pattern piece. I would machine sew the blocks using the tutorial found on this board rather than sewing them by hand. Say a prayer, then cut the pattern pieces and zigzag all the cut edges. If there are any facing pieces, cut them from unpieced yardage. Construct the jacket & line it.
I would also look in quilting stores for a jacket pattern suitable for quilted fabric.
Here's one from Nancy'S Notions:
http://www.nancysnotions.com/product...ket+pattern.do
Maybe someone will have an exact pattern.