i would like to build a linux based MAME system . nit sure where to start have a decent pc to use but not sure which distro to use or where to find the roms . any help is greatly appreciated

Any distro would do - I think there's even a version of MAME that will run without X.
The ROMs are all copyright material so in most countries unless you have an actual ROM, you're not supposed to be playing with an electronic copy - unless of course the original copyright holder has put it in the public domain. If the copyright holder was a company which no longer exists then you can do what you wish as long as they didn't sign the copyright to anyone else who currently has a legal representative. It's a rats nest like most legal things, which is why distros may have MAME as an installable package but don't even tell you where to go hunting for ROMs - you're on your own there.

well the thing is i`m looking for a small distro only to run mame and maybe firefox or opera for searching i would mostly just use it just for older arcade games

Maybe look at a distro like 'puppy' which is trimmed down to run on ancient machines. A typical distro like Debian is pretty bloated these days and it takes time and effort to trim it down.