I sprayed my cases internal panels metallic blue (both sides)
Was a lot more expensive that I thought - used 9 cans I think.
But my case is massive and metallic needs 2x primer 2x base, 3x top 2x lacquer.
Most people that do matt black, just need the one can.
The black panels I did needed two cans as I needed to prime the bare aluminum of my S80B
It helps if you have access to a dust free, windless, ventilated area, (garage)
But preparation (striping the case - so you have limited internal corners)
And giving yourself enough time is the key.
Took a week of lunch hours to do mine (in a walled patio behind my old office)
It's not perfect as I had a few issues with the lacquer (which is optional).
My fault as I tested out the paint first before I used it on my case.
but used to much lacquer and didn't leave it long enough to dry.
Final coat showing damage
Starting point - internal and external panels removed
Painting finished
Was it hard - NO (but had the time to do the prep)
Am I pleased that I did it - YES (was a really rewarding week, untill I messed up the lacquer)
Would I do it again - YES (if black as that's easy) NO (if metallic - get a car body shop to do it for you)