Material to build Project Box? Answered

I've finished a couple of circuits and I keep bumping in the same problem. Making a decent box for them. Its hard to find anything ready to use and i'd rather make my own stuff.

What your advise on wich materials to use to build stuff?  
I think it would be an awesome instructable, having someoen explain how to make your project a little bit more permanent with its on caseing.

Acrylic tends to be a bit expensive.
someone suggested ABS plastic but i cant seem to find anyone selling ABS plastic sheets near by.

Thanks!