thats the question.

i am thinking of building a 2x10 cab. just simple sealed enclosure with two really good speakers.

if not im just going to buy a cheap used 2x10.

any advice?
if i built the cab to specs matching speakers will it not sound as good as one i buy? except ill get to pick the speakers and wood right? or am i totally naive?
If you happen to find an old used cab with really good speakers - you'd better buy it.

If you happen to have your ways around making something on your own - you'd better build it. Pick a couple of GOOD speakers, buy some plywood, hardware and tolex and start with a drawing. You can build a finest one this way and it will definitely sound better if you use quality materials unlike those in mass production.
Building cabs is rather rewarding as it's not so complex.