1. I get out the proven-to-be-good GuitarFuel wire harness, from my supply inventory. If I'm not interested in using an AC adapter with my amp, I choose the SD-2W harness. It's easy to install, and it works great. If I want a little more from my amp and the convenience of plugging it into the wall, it's the SD-MAH3 for me. In my opinion, the GF harness is the best available. It may be a couple bucks more than some of the others I see on some of the web sites, but the quality is top notch, and I don't have to screw around with anything . . . it comes to me ready to install.
2. Next, I select the cigar box I want to use for my amp . . . and, my selection might be something other than a cigar box, if I find something so unique that I cannot live without it, such as a vintage radio. But usually it's a cigar box. The box must be large enough to accommodate the harness, and speaker of choice. My favorite is the 'Acid' box, but, I have a drill press and Forstner bits, so I can drill the necessary holes deep enough to accommodate the switches and plug connectors. The sides and front of the Acid box are much thicker than many other possibilities.
3. While I was doing #1 & 2, I was also thinking about the design, and now I'm ready to move forward. Where will the controls and connectors be located? What about the sound hole opening over the speaker? What other special items to consider, e.g., handle, knobs, latch, feet, graphic application, and etc. The controls should be easily accessible and the speaker opening should be in an area that pumps sound toward your audience. You can make a control location template, which will make your job easy. However, changing things around gives originality to your builds, so you may want to forego the template idea. And, the harness leads are long enough to allow for any possible location idea you may have.
That's about as complicated as it gets. So, grab your tools and go to work . . . all you'll have is fun.
Following are some design ideas you may find useful.
And, for a closer look at the detail of the amps I build, please go to the right hand column of the home page, scroll down to the 'amplifier' logo, and click on any picture to be taken to the post explaining the build.
I hope this tutorial has been helpful and inspirational.