I just read Chicory’s answer and I think she is correct that the OSB will be too heavy. And why do you need it on both sides anyway?I think yes a sheet and a half will do it but it will be tight and you will need to piece strips together for the upper part of the inside (around the window).
Check I have understood correctly (see sketch).
I started a cutting diagram but realized I wasn’t confident enough to get it perfect.
Basically it works this way:
- From the full sheet cut a piece that fits the whole door and then cut out the window. Ideally cut out the window so you can keep that piece undamaged so it can be the actual hinged shutter. That is not easy. Alternatively do the door I. Two pieces (top and bottom) which makes it easier to cut out the window.
- Preserve the L-shaped scrap as you will need to rip that down to cover the area around the window on the other side of the door.
- From the half piece cut the bottom of the door (roughly 29x26 if I understood your picture).
- Cut scrap into pieces to frame the window on the inside of the door (I say inside because ideally fewer joins on the side that is to the weather).
Hope that helps.
View attachment 4180142