new to koi need help in choosing a pond liner

Im moving to a townhome that only has a 18' x 22' yard. I was
thinking of getting one of those hard liners and building a raised koi
poind. I want to get at least 3 - 5 koi what size of a liner do i
need. remember I want one that is already molded.

Also if some one can point me to a site that might have a setup like
the one i want with the FAQs and howto set it all up that would be
great.

Thanks,

Rigz