A cabinet is definitely going to be easier to build than a bass
Check the stickies in the Amps forum section, there's a whole bunch of DIY projects I'd start looking at, plus you need to get acquainted with how speakers and amps work etc. For example it's best not to mix cabinets w/different sized speakers etc.
It's all in there, just have to start reading. And then post questions here and those w/more experience and knowledge can help.
Good luck and have fun
