Making a cab is no big deal if you have suitable skills and equipment. You need to be prepared to do the job properly, though otherwise you might just as well get a second hand cab off trademe.
Assuming you have those things, the biggest pitfall is accuracy. Getting everything square, straight and to even dimensions is the hard part. Other thanthat, just copy the design of a known good product and think about all the factors mentioned here. You can find dimensions on the Marshal/Mesa/Orange websites and sometimes internal pictures.
Materials: For solid wood, go with good old pinus radiata, but be aware that its not very strong, so needs reinforced joints and dent protection. Best allround material I've seen is 17mm plywood labelled "Wayang Brand Ivorywood" I don't know what it really is. Plywood places have it or can get it.
Carpet isn't cheap or easy to get, I've found. But boat upholstery vinyl is and comes in purple
(also my favorite for cabs) amongst other colours.Good speakers will likely be the most expensive thing, and seem unusually hard to get. British made Celestions, Webers, Eminence, Jensens (if you're desperate for vintage) or Peavey Black Widows if you're rich enough.
If there is suitable interest, I could put together some 2x12 kits, so you don't have to worry so much about the hard parts or expensive tools. PM me, anyone who is interested in a finished or kitset cab. If there are six cabs worth of takers I'll work out a price with a donation to NZG's worm fund included.
