Some things I learnt (got wrong) when I built my own 1x12.
The size and thickness of the baffle board effects the sound, as does the way it's suspended or mounted into the cab. It can be quite thin and it needs to vibrate.
Do not build the cab from the thickest, heaviest plywood you can find.
You can use 1/2" baltic birch for a 1-12" baffle. Might even get away with 3/8".
Mounting it as a 'floating' baffle (fixed only top and bottom) helps it resonate, too.
If it's an open-back, use a resonant solid wood for the cab, like pine, spruce, poplar, or any other tonewood. I've used normal DIY solid pine, but I must have looked like a real clown pulling out every single piece of wood, checking it for warping, and knocking it with my knuckle to see how it sounds. It works though; I got a solid, good-sounding cab out of it. Course, when you cover it with glue and tolex, you dampen all that, but tweed enhances it.
If you do closed-back or ported, and want all the sound to come out the front, use good 3/4" voidless ply. Make a good stiff cab. Voidless is important for the baffle, too - the thing about baltic ply is it is usually voidless, the cheap stuff you get at the DIY is anything but voidless. Voided, so to speak. Then you get layers of ply vibrating against each other - not good. You could look for a long time before you realize that annoying buzz is coming from
inside the baffle.
My brother built a 1-12" baffle out of a soundboard from an old grand piano. Very nice. Stuck it in a walnut cab, made from a single 40-year old piece. Put a 5e3 that I built for him in there. Beautiful amp, visually and sonically. Here's a shot:
http://www.stevenhusting.com/Amps/other/foot_5e3_2.jpg just my 2 cents worth
steven