Is there any tutorial about creating a custom HUD?

Search is your friend:
http://ghost.halomaps.org/tutorials/#ui
&
http://hce.halomaps.org/index.cfm?fid=1214
Hope this helps!

Of course, I was meaning totally custom HUDs and yes visors, health/shield bars, ammo meters etc. If you find any and/or create one for me that would be most grateful.

K, thx guys.

Visor:

After compiling your 1024x1024 bitmap, scroll down to the second drop-down menu and select 32-bit color to have smooth alpha, even if your alpha is only one color, since it gives me a lower-res bitmap when i don't. After changing it, save it, and compile it again. This time tool will take the data from the bitmap tag(i think).

Then, in any (unit/weapon/grenade)_hud_interface tag, specify the bitmap. I'd recommend a unit_hud_interface tag so that it shows up regardless of what you have equipped. You put it at the very top, in HUD Overlay.

As for the weapon/grenade hud tag, put it in static elements.

From Quagmirian(or Philly on halomods)'s tutorial, the settings should be: both offsets are -10, and both (width/height) scales shouldbe 0.6276. I don't know if you use "Use high-res scale" instead of changing the w/h scale, but it went to half the bitmap size last time i did.