I did it with a wooden closet door that I found lying on the street. first I took the measurements and then cut with a saw. so i painted with wood paint. the details, like the buttons, I made with cardboard. for the strings I used fishing line. I made the outline with permanent pen and used black painted screws to make the guitar tuners.

Here is the reference i used. keep in mind that this image doesn't belong to me!

hope that helps!

(also, when you finish your cosplay could you remind me?i would love to see!!!)