Hi
KayEhm,A trommel is just a rounded moving screen (this is an underestimation I guess
) but instead of hand classifying , you just let the trommel do the job.
Also this depends on your material being run, if you have a lot of clay, this is where the trommels shine. They give those nasty clay cobbles a nice ride and showers
a massive torturing machine if you say so !! On the other hand, if your gravel is "clean" enough, then a regular highbanker or power sluice (if you're permitted to use such machines ) would be sufficient to get the gold.
You ask whether to buy or build, well that also depends on your budget and access to tools and your craftsmanship ! A trommel is not that hard to build yourself provided you meet the aforementioned criteria. If you have the time and the right tools, you can put one yourself. If you don't want to waste time building, testing, modding...etc then buying a trommel is much quicker to get you shoveling
There are many one person units on the market with varying degree of gold recovery efficiency and price tags.