Wood choice and all other considerations such as joints, humidity level, etc. aside, the thickness and length of the sides do more to determine the potential overall tone, pitch, and volume of a box call than any other factor. I prefer slightly thicker sides, a purely personal preference, as I figure it makes for a sturdier call that can withstand more abuse in the field, and I'd rather be thinking about hens and gobblers than worrying about my equipment. And while thinner sides can, in some cases, result in more volume and higher pitch (particularly in "routed-out" calls such as boatpaddles), it must be remembered that more mass also equals more volume and sustain, to a certain extent. It also means a "tougher" call for field use. Of course, if you sit on one (been there...done that), it'll break no matter what the dimensions!

Cutting

Once the stock has been resawed to the appropriate thickness, it can be cut to length. I usually just size it against the base it will be attached to; then, because the wood in now so thin, I simply cut it with a utility knife (although I have stacked multiple blanks on top of each other and cut them en masse with the backsaw in the miter box. Whatever I use, I like to cut it just a tad proud (by 1/8", or 1/16" at each end) so that I can sand it flush with the base and end blocks after the call's been assembled. TIP: Some luthiers split wood along the grain of their guitar bodies before final shaping is done in order to work with the wood's natural strengths and weaknesses. This is not a bad idea when making an assembled call as well, as a weak spot in the grain will inevitably affect the call's final sound in terms of volume, pitch, tone, sustain, etc.

The next step is to shape the radius. Generally, I shape it so that the ends are about 1/4" or less lower than the middle; I have found the call easier to work with and tune if the radius is not too extreme, since a high peak will seat the lid at an angle over the box and interfere with the call's tuning and consistency. Over time I've made a couple of plywood patterns and, once I've split the blank along the grain to get it closer to its final width, simply lay a pattern on the stock, mark it, and shape it with a Surform, sanding block, power sander, or utility knife.

Shaping

The top edge of the side where the lid scrapes across is the rail. This should be rounded over slightly with a medium grit (150-180) sandpaper. Some woods (such as cedar) may need to be sanded to a finer grit, but I've found paper in this range tends to produce the best results on the woods I use. The rail needs to be smooth so that the lid can be scraped across in a single fluid motion without catching or grinding.

Finish Sanding

As with the other parts, it's a good idea to go ahead and do most of the finish sanding now, before the call is assembled--it's much easier. For the non-striking surfaces I start with either a coarse grit (80, for really rough wood), or a medium grit (120, for fairly smooth wood). If I want it really smooth I'll use a few passes each with 120, 150, 220, and maybe even 320 or so). Most of the time, however, I quit at 220.