You use a breadboard to try out designs and change components easily. They have push-fit connection terminals that make for quick assembly but not for long-term robustness. Once you're happy with the design, they you'd either make your own PCB, or transfer it to strip-board. It all depends on how compact you can make the design as to how big a box you need to fit it in.
All the micro-pedals do without a battery ability, and use surface-mount components for the most compact footprint. With mostly discrete, and all hand-soldered components, you're unlikely to ever get down to that generic micro-size box, but you should be able to manage to squeeze most pedals with 1-3 knobs in a small MXR/Boss sized box. If you've got 6 knobs on a pedal, then their physical size, and the spacing need to cleanly access each knob, determines the minimum size of box you'll need.