Its fairly rare to make your own radiator, i dont think iv ever seen a DIY radiator, if you have any old pictures or examples id love to see, im sure you could buy a heatercore for the a similar price to the materials and it would certainly outperofrm it.
Iv seen intercoolers that have been done,for use in phase change systems some pretty clever but none that would work as effectivly as a heatercore or radiator.