I myself don't actually scratchbuild cabinets, but I do tend to have lots of projects going on at the same time.
Right now I have 10 projects (Defender which just needs a PC, Stargate, Star Wars cockpit, Turbo upright, Sprint 2, Stunt Cycle, Amazing Maze is back to project status, Battlezone, Robocop pinball, which doesn't actually need much work, and a cocktail).
I did actually manage to finish several projects this month, but promptly sold and traded them.