As protoss:

The safest thing to do as protoss is to build at least one sentry as early as possible from your first gateway. This will let it save up energy so that you can cast more force fields.

If you do this and also scout the roach rush you should be prepared to place the force field well (trap 1 or two roaches on your side of the ramp so that you can pick them off).

Since all maps except scrap station (which has a really long rush distance) have small ramps this is probably the only thing you need to do to beat it.

Is the rush really done that often? Doesn't feel very strong against protoss because since the ff at the ramp totally negates it.