Aluminum panels

Hello,

Can someone please direct me to some companies that make the aluminum
(i think its aluminum) panels? Do you call these companies and tell
them what type of plane you have and there is a standard panel size...
then let them know what size holes you want? Or is this something that
you take the plane down and do an exact fitting? Any idea what one
pays just for the panel? (not any install)

Thanks,

-dr