one suggestion
I was going to build myslef a cab about a month ago, then I found out about avatarspeakers.com I was looking for a 2x12 combo with celestions and marshall was selling thier least expensive with the celestion GT-75 for $460. I checked out other cabs (mesa, etc) with celestions on ebay and found them to be only about $100 less.
I checked into making my own. I don't have any tools, so I'd either have to borrow them or buy them. I would have to try to figure out how to design it. I figured the wood would cast me about $100, a celestion geenback $100, a celestion vintage 30 $120. Then there is the hardware $50 or so, and some sort of covering $20 for something cheap probally - now i'm up to $340 for my cabinet!!! Avatar speakers sells 2x12 custom made cabinets like the one I was going to buy for $350. They even sell cabinets without speakers but you'd have to email them for the price.
I would seriousl suggest looking into this company, because they just have amazing deals. I just got my cabinet yesterday (6/25/04) and its looking and sounding pretty promising so far. I'm gonna be firing it up again later today when the nieghbors are already awake.
If you really want to build your own cab and don;t have the speakers avatar will beat anyone's prices on celstions (and probally eminances and jensens but I haven;t really looked into that)