I used 3/4 inch prefinished ply that I found in the scrap bin, so really anything big enough, and strong enough to make your shelf will work.
Step 1: Cut sides
I took the extra step of rounding off the top front corners with the belt sander just for aesthetics, but this is by no means necessary.
Set the fence on the table saw to your desired width and rip away, when cutting the sides to length, I used the cross cut sled, but you could use the band saw as well, or just be super super careful. If you are not comfortable and knowledgeable cross cutting on a table saw, I highly recommend using the sled to save yourself stress and potential injury.