Only know the US brands for this, so Google.as needed.
For small holes #2 Whitney or knockoffs thereof is an obvious choice. The Whitney Jr #5 has tiny punches with the tolerances already worked out for cold work in thin metals.
For bigger holes ironworker punches are nice and are often found used in decent shape. Usually these are to a standard size based on the ironworker brand so find some punch/die sets then make an adapter for them. They're designed to go through seriously thick metal mild steel.
For huge holes in thin stock Greenlee chassis punches or similar two-part bolt together sets work fine, take them apart and use bolts to mount the two pieces solidly so they meet properly on your press. I've used these by hand, by hydraulic press and even with an arbor press (small ones only). The tolerances are designed for 16ga or so, other thicknesses may not cut as clean.
All punches can be expensive purchased new, but that's what the used machinery market is for. Bought ironworker punch sets from a scrapyard(!) by the pound, my GreenLee set for $20 (8 punches, one needed work) and a box of 10 Whitney #2 die-punch sets for $15. Usual craigslist/Ebay/garage sale sources are worth a look.
For those near southern NJ USA, the best used source for such things is Fazzio and Sons in Glassboro, good selection of ironworker and all kinds of other used tooling, though their prices aren't as good as above.
If you really want to make your own punches grab one of the many diemaking book pdfs off of books.google.com first, they're pre-1919 but the design info is still good. It's really not worth doing unless you're looking for an unusual shape that's not commercially made (e.g.hearts or other decorative shapes).
Hope that helps.
Sonny
