If you have a regular need to cut down sheets of plywood, you're undoubtedly already thinking of how great it would be to have your own panel saw. You're right, of course, and here are a few examples to nudge you in the proper direction:

Vertical panel saw by Alexander Birnie

Homemade Panel Saw From Pipes And Castors by WayOutWest Blowinblog

Homemade panel saw with clamps storage by BiggeDink

Homemade Vertical Panel Saw by Radim04

homemade panel saw by joe henry