I've often thought about doing this myself, but I've never got round to it, being too busy working on existing machines to make a new one from scratch!
I made a homemade non-suction-losing 5 stage hepa cyclonic v
Here it is. All the elements of a cyclonic vac: cheap plastic, 12 amps, stretch hose, hepa, strong suction that doesn't leave you, LOUD, overheating issues, clear windows, EZ empty, nasty washable filters, etc. Though it does work very well. Took half a year to design. I call it the Stage 5