A reader, Ray asked about the thickness of box sides relative to the proportions of the box. The boxes I make range in wall thickness from 5/16" up to 5/8"depending on size and the particular look of the box. There are no hard and fast rules, but you have to admit that a small box made of thick stock seems rather absurd as there is little available space inside.
Normally, I just make boxes. You get a feel for proportion after you've made a few as to what works and why. A bit of time at a craft show or gallery will give you a lot of information. Check out another box maker's work, and make your own evaluation as to how you would do things either alike or differently.
When I teach, students will invariably ask about proportion, usually leading to discussion of the golden mean or Fibonacci sequence. I ignore most of that regarding it as irrelevant. I have discussed proportion previously on the blog and you can find those posts
here. I prefer to think about these things: Where will it be put? What will be put in it? Who is it for? How will it be used? Those are far more important factors than an artificially derived set of proportions, and so far I think things have worked OK. In addition to the who, what, when and how, your choice of hardware often dictates the thickness of box sides. For instance 10 mm. barrel hinges require thicker sides. But hinges like those fine hinges made by Brusso work best if they are mortised on three sides, and thus require box wall thicknesses of 7/16" or greater.
I have a new article out in Woodcraft magazine, June/July, 2010 about the mixing and matching of woods. The article is illustrated with a number of my boxes from earlier publications and some of my furniture as well.
Today I began work on a very small walnut chest of drawers with sides that taper toward the top. "How does one make sides that taper toward the top?" You ask. 
A reader, Ray asked about the thickness of box sides relative to the proportions of the box. The boxes I make range in wall thickness from 5/16" up to 5/8"depending on size and the particular look of the box. There are no hard and fast rules, but you have to admit that a small box made of thick stock seems rather absurd as there is little available space inside. 
My book, Complete Illustrated Guide to Box Making has been translated into German and published in a hardbound edition. Kästen und Schachteln: perfekt konstruieren und bauen by Doug Stowe is now available for purchase in Germany. The title translated into English means Boxes and boxes: design perfectly and build. Perhaps one of my German readers will help by explaining the difference between Kästen and Schachteln. The book is published by HolzWerken.
