Indoor or outdoor shutters?
Here's a tutorial for plantation shutters if you're looking for indoor: https://providenthomedesign.com/2014/10/30/diy-plantation-shutters/
Shutters othe Hometalkers built
Something like this? https://www.frugalfamilytimes.com/2019/08/easy-diy-wood-shutters-for-under-10-pair.html?m=1
Do you want shutters mounted over the window that actually function to open and close, or shutters at the sides of the window for decorative purposes only?
Here is an idea for working indoor shutters:
Here is an idea for outdoor shutters:
It all depends on your woodworking capabilities and imagination. Others have given some good solutions.
here are so many ideas https://www.pinterest.com/search/pins/?q=shutter%20panel%20for%20windows%20diy&rs=typed&term_meta=shutter%20panel%20for%20windows%20diy%7Ctyped
These use an old wooden blind for the slats. Neat idea if you like upcycles. https://www.hometalk.com/37084904/decorative-window-shutters
You could just use a piece of board the size of the window and cut in half then attach hinges on the sides and a lock in the middle
I have a very easy & affordable tutorial: https://bachelorettepadflip.com/2014/06/30/diy-cedar-shutters/
Best way is to build board and batten style half the size of the window +1" horizintally and +2" vertically to overhang the sides by 1"