making a porous face with symetry

Saeed

I wanna model a cylender in gambit which its lower face has e.g 20 hole ,but also want to use a symmetry which means I plott a rectangle and impose a symetry on the left side => it is cylender;but if I make any hole in the lower side of this rectangle it becomes a ring, Does any one have any Idea for making this holes and also using symmetry????????? thanks in advanc