what's a good size to port either a 12'' RE SE or a magnum?

i am gettin an SE soon as i am changing my whole system again. But i would like to make a box that i can use with the SE and then if in a couple of months if i decide to get either the Magnum (most likely) or XXX use the same box cuz i am planning to do some glassin to it.

Thanks.

PS - portin it to ~32hz