Custom made drawer are not as hard as you think. I mostly but sheets of 2sided finished ply and make my own but in the case I was making one drawer and I decided to use pre made drawer sides. I needed 2 3/4" high sides. So I bought a 6" tall piece and cut it down to size so I could have the finished top part. If I had used a 4" side and cut down I would have lost that. I used a spare piece as a Template for the dado cut height. I did not have to switch to a dado blade set(set of blades u stack together to cut wide slot in wood)because a simple two pass cut was enough for the drawer bottom.
I have been asked several times about how I get all those shelf pin holes lined up so strait. A shelf pin jig of course!!! But shhhh I didn't tell you..