Have spend some time in the champions system (and even a tiny battle takes some time in the champions system), I divide traps into "targetted" and "area of effect". If something shoots at or strikes at the PC, that is a to-hit roll. If something big effects everyone in a given area, that is a reflex save. Weapon traps are to hit, pits and 10' x 10' blocks are reflex save. A big boulder could go either way, depends on how you write or DM it. Feel free to run any trap any way you want. Just make sure it is some risk, but not instant-death-no-to-hit-or-save (unless you name is Acerak).