well to cut a hole in a sheet of metal you can use various methods:
a rotary cutter disc such as a dremmell
a hole saw which is basically a type of drill bit which cuts holes
a drill and connect the dots
a juniour hacksaw
a hacksaw
some snippers
some motorised pincers
sand through the sheet metal (warning may take an excessive amount of time)
practice your 1 inch punch until you can punch through sheet metal
stab it with something (screwdriver may work well)
use a nail to scratch out the outline and continue to repeat the circular movement until either the nail is filed down or the sheet metal is scratched through
use a blow torch to melt a hole
use a house hold pair of scissors
use a machette
sand away the paint from the area then place a cup of water upside down on it and wait for it to rust through......