The ornamental design for a rooffield vent, as shown and described.
FIG. 1 is a top, front, perspective view of a roof field vent showing our new design;
FIG. 2 is a top view thereof;
FIG. 3 is a bottom view thereof;
FIG. 4 is a front view thereof;
FIG. 5 is a rear view thereof;
FIG. 6 is a side view thereof; and,
FIG. 7 is another side view thereof.
The broken line showing of portions of the roof field vent is included for the purpose of illustrating environmental structure and forms no part of the claimed design.