Building your own gear is hardly cheaper than getting new stuff, let alone 2nd hand. It's hard to beat big companies who buy parts and materials in huge quantities, and have their products assembled in countries with low wages.

Search Ebay if you're in the US. Sure, you can build a 1x15 cab for USD 200, but a used, ready made cab can be had for about the same cash. Cheap second hand is better than cheap DIY. Besides, you'd be able to use it right away, not having to deal with power tools, soldering iron, wood sheets, glue, clamps, screws, sawdust on the speaker, foam gaskets, silicone caulking, carpet finish or polyurethane coating, protective corners and linings, grilles, tuning measurements, power testing, air leak checking etc., etc., etc. all at the risk of ending up with a bad sounding cabinet. The real advantages of building sound gear yourself are:

• You want or need something that's simply not available commercially (which probably has a very good reason)
• You can specify your own materials, determine your own dimensions etc.
• You can make ik look like nothing else

You CAN build cheaper than the big boys, but this is only valid for high-end cabinets. You can build a very high quality "boutique" guitar or bass guitar cabinet for the price of a mid-range one. Still not at all cheap, but affordable, high quality. Needless to say, you need a lot of experience to do this. I hope to arrive at this level some day .