The Dimensions are going to the same as my Mesa 4x12- 30" wide by 32" high and 14" deep. After checking out as many dimensions as I could find, it seems that this is a good average size. I drew up some sketches, and planned out how to make the whole thing from one sheet. I MAY end up trying to finger joint the corners, but for now, I'm thinking I'll keep it simple and use butt joints, glued and screwed. I also plan to tolex it, which will be a first for me.
I downloaded Sketch Up earlier today and gave it a shot. Heres a pic of the basic structure;

Once I figure out what hardware I'm going to use (handles, jack etc) I'll add those onto the drawing.
I'll update this as I go along. It's probably going to take a while, because the only place I have to work is an unheated garage. So all the gluing and whatnot can't really start until it warms up a bit.